Help I have this question and I don’t know what the value of a would be

If f(x)=x^3 and g(x)=2x+7 when g(x)=-5

Need plz been trying to do it for a long time and still haven’t succeeded

Ahovercraft takes off from a platform. its height (in meters), xx seconds after takeoff, is modeled by: h(x)=-2x^2+20x+48h(x)=−2x 2 +20x+48 what is the maximum height that the hovercraft will reach?