-3•f(-8)+7•g(2)= ???

First, find f(-8) and g(2). For f(-8), go to x=-8 on the graph and find where f(x) is at x=-8. f(-8)=-2. Repeat this process for g(2). g(2)=-4.
Now the expression reads, -3(-2)+7(-4). -3*-2=6. 7*-4=-28. 6-28=-22
Hope this helps!!