Final answer:
The correct expression for applying the distributive property to −10(7.1+12) is −10×7.1+10×12.
Step-by-step explanation:
When applying the distributive property to the expression −10(7.1+12), Mary would use expression (a) −10×7.1+10×12. This correctly applies the distributive property, which states that a(b + c) is the same as ab + ac. So, when distributing the −10 across the terms inside the parentheses, you multiply −10 by each term separately, and then sum the products.