I'm assuming the given function is f(x) = 15x^2 + 10x.
If so, then,
f(x) = 15x^2 + 10x
f(x) = 15*(x)^2 + 10*(x)
f(-1) = 15*(-1)^2 + 10*(-1) ... note how x is replaced with -1
f(-1) = 15*(1) + 10*(-1)
f(-1) = 15 - 10
f(-1) = 5
Therefore the answer is 5