Simplify: 3 times 7, minus 4 times 7, minus 5 times 8.

1. Multiplication comes before subtraction, so multiply each pair first. 2. 3 times 7 equals 21, 4 times 7 equals 28, and 5 times 8 equals 40. 3. The expression becomes 21 minus 28, minus 40. 4. Subtract left to right: 21 minus 28 equals negative 7. 5. Finish with negative 7 minus 40, which equals negative 47. 6. Subtracting the last two products from each other before subtracting from 21, instead of working strictly left to right, would produce a different and incorrect total. 7. Treating the final answer as positive 47 forgets that a negative result stays negative once both subtractions are carried out. _Source: OpenStax Prealgebra (CC BY 4.0), Ch 3 "Integers", section 3.3 Subtract Integers_