Answer
a. $8x-3$, b. $2x-17$
Work Step by Step
We are given that $f(x)=5x-10$ and $g(x)=3x+7$.
We know that $(f+g)(x)=f(x)+g(x)$ and $(f-g)(x)=f(x)-g(x)$.
Therefore:
$(f+g)(x)=(5x-10)+(3x+7)=5x+3x-10+7=8x-3$.
$(f-g)(x)=(5x-10)-(3x+7)=5x-3x-10-7=2x-17$