1. Simplify inside the bracket: $$(-15) - (-3) = -15 + 3 = -12$$ 2. Multiply by 7: $$7 \times (-12) = -84$$ 3. Divide by 4: $$\frac{-84}{4} = -21$$ 4. Simplify inside the parenthesis: $$28 - \frac{8}{4} = 28 - 2 = 26$$ 5. Square: $$26^2 = 676$$ 6. Add the results: $$-21 + 676 = 655$$ 7. Simplify powers and terms inside brackets for 13: $$-5^2 = -25$$ $$3 - 9 = -6$$ $$4 \times (-6) = -24$$ $$\frac{49}{-7} = -7$$ 8. Compute bracket: $$-25 - (-24) - (-7) = -25 + 24 + 7 = 6$$ 9. Multiply by -7: $$-7 \times 6 = -42$$ 10. Subtract from 24: $$24 - (-42) = 24 + 42 = 66$$ 11. For 14: $$-13^2 = -169$$ $$15 - 6 = 9$$ $$-5 \times 9 = -45$$ $$\frac{-45}{9} = -5$$ $$-5 - 3 = -8$$ $$8 \times (-8) = -64$$ 12. Add inside bracket: $$-5 + (-64) = -69$$ 13. Multiply by -2: $$-2 \times (-69) = 138$$ 14. Add all: $$-169 - 138 = -307$$ 15. For 15: $$-4 + 5 = 1$$ $$\frac{1}{2} = 0.5$$ $$0.5^3 = 0.125$$ $$6 \times 2 = 12$$ $$9 - 12 + 2 = -1$$ 16. Sum inside bracket: $$0.125 + (-1) = -0.875$$ 17. Multiply by -2: $$-2 \times (-0.875) = 1.75$$ 18. For 16: $$-\frac{1}{4} - (-\frac{3}{7}) = -\frac{1}{4} + \frac{3}{7} = \frac{-7 + 12}{28} = \frac{5}{28}$$ 19. For 17: $$\frac{2}{5} - \frac{6}{7} = \frac{14}{35} - \frac{30}{35} = -\frac{16}{35}$$ 20. For 18: Convert mixed number: $$-2 \frac{3}{8} = -\frac{19}{8}$$ $$-\frac{5}{7} - (-\frac{19}{8}) = -\frac{5}{7} + \frac{19}{8} = \frac{-40 + 133}{56} = \frac{93}{56}$$ 21. For 19: Convert mixed numbers: $$2 \frac{1}{5} = \frac{11}{5}, \quad -4 \frac{5}{6} = -\frac{29}{6}$$ $$\frac{11}{5} - (-\frac{29}{6}) = \frac{11}{5} + \frac{29}{6} = \frac{66 + 145}{30} = \frac{211}{30}$$ 22. For 20: Convert mixed numbers: $$-1 \frac{3}{4} = -\frac{7}{4}$$ $$3 + (-\frac{5}{6}) - \frac{7}{4} = 3 - \frac{5}{6} - \frac{7}{4} = \frac{72}{24} - \frac{20}{24} - \frac{42}{24} = \frac{10}{24} = \frac{5}{12}$$ 23. For 21: Convert mixed numbers: $$-1 \frac{3}{8} = -\frac{11}{8}, \quad 5 \frac{1}{8} = \frac{41}{8}$$ $$4 - (-\frac{11}{8}) - \frac{41}{8} = 4 + \frac{11}{8} - \frac{41}{8} = \frac{32}{8} + \frac{11}{8} - \frac{41}{8} = \frac{2}{8} = \frac{1}{4}$$ 24. For 22: $$8 \times (-\frac{3}{4}) = -6$$ 25. For 23: $$\frac{4}{15} \div (-\frac{1}{3}) = \frac{4}{15} \times (-3) = -\frac{12}{15} = -\frac{4}{5}$$ 26. For 24: $$(-3) \div (-\frac{3}{5}) = -3 \times (-\frac{5}{3}) = 5$$ $$5 \times \frac{7}{15} = \frac{35}{15} = \frac{7}{3}$$ 27. For 25: $$(-\frac{1}{4}) \times 80 = -20$$ $$-20 \div (-\frac{4}{5}) = -20 \times (-\frac{5}{4}) = 25$$ Final answers: 12. 655 13. 66 14. -307 15. 1.75 16. \frac{5}{28} 17. -\frac{16}{35} 18. \frac{93}{56} 19. \frac{211}{30} 20. \frac{5}{12} 21. \frac{1}{4} 22. -6 23. -\frac{4}{5} 24. \frac{7}{3} 25. 25