Answer :
We will first find substitute x = -2 into the function and then evaluate
f(-2) = (-2)² + 5(-2) - 12
= 4 - 10 - 12
= -18
Then substitute x = 1 into the function
f(1) = 1² + 5(1) - 12
=1 + 5 - 12
= -6
Then
Use the formula;
[tex]\frac{y_2-y_1}{x_2-x_1}\text{ =}\frac{f(b)-f(a)}{b-a}[/tex][tex]=\frac{-6+18}{1+3}[/tex][tex]=\frac{12}{4}[/tex]= 3