1. The problem is to find the number that replaces the box in the equation $\frac{3}{4} = \frac{\Box}{20}$. 2. We use the property of equivalent fractions: if $\frac{a}{b} = \frac{c}{d}$, then $a \times d = b \times c$. 3. Applying this to our problem: $3 \times 20 = 4 \times \Box$. 4. Calculate the left side: $3 \times 20 = 60$. 5. So, $60 = 4 \times \Box$. 6. To find $\Box$, divide both sides by 4: $\Box = \frac{60}{4}$. 7. Simplify: $\Box = 15$. 8. Therefore, $\frac{3}{4} = \frac{15}{20}$.