You have to remember that [tex](f-g)(-5) = f(-5) - g(-5)[/tex] , then first evaluate each one separately, and finish by subtracting them.
[tex]\begin{aligned}(f-g)(-5)& = f(-5) - g(-5)\\[0.5em]&= [ (-5)^2 - 4(-5)] - [2-3(-5)]\\[0.5em]&= [ 25 +20] - [2+15]\\[0.5em]&= 45- 17\\[0.5em]&= 28\end{aligned}[/tex]
