Question 179402
What you are being asked to do is evaluate an expression/function at a specific value of x.

{{{f(x) = -5x +8}}} at the vlaue{{{x=-3}}}
So plug in -3 for x everywhere in the equation. Then solve it
{{{f(x) = -5x +8}}}
{{{f(-3) = -5(-3) +8}}}
{{{f(-3) = 15 + 8}}}
{{{f(-3) = 23}}}

Use the same process for the second problem.
{{{f(x)=3x^2-4x-3}}} at x=-1
{{{f(-1) = 3(-1)^2 -4(-1) - 3}}}
{{{f(-1) = 3(1) + 4 - 3}}}
{{{f(-1) = 3 + 1}}}
{{{f(-1) = 4}}}

get it?