1. **State the problem:** We have 6 300 kg of building sand and want to convert that to grams in standard form. Then, given one grain weighs $7 \times 10^{-5}$ g, find the number of grains in the total sand. 2. **Convert 6 300 kg to grams:** 1 kg = 1000 g, so $$6300\text{ kg} = 6300 \times 1000 = 6,300,000 \text{ g}$$ 3. **Express in standard form:** $$6,300,000 = 6.3 \times 10^{6}$$ 4. **Find number of grains:** Each grain weighs $7 \times 10^{-5}$ g. Number of grains = total mass / mass per grain $$= \frac{6.3 \times 10^{6}}{7 \times 10^{-5}}$$ 5. **Calculate:** $$= \frac{6.3}{7} \times 10^{6 - (-5)} = 0.9 \times 10^{11} = 9 \times 10^{10}$$ 6. **Final answers:** a) $6 300$ kg in grams = $6.3 \times 10^{6}$ g b) Number of grains = $9 \times 10^{10}$ grains