Question

If f(x) = -3x + 2, what are the values of m and b so that F(mx+b) = 2x-3?

Answer 1

I assume you mean f(mx+b) = 2x-3 In other words, a lower case f, which they tell us is f(x)= -3x+2

Answer 2

f(mx+b) means replace the "x" in f(x)= -3x+2
with the more complicated expression (mx+b)
you get
f(mx+b)= -3 (mx+b) + 2
and that is supposed to equal 2x - 3
-3 (mx+b) + 2 = 2x - 3