Question 162256
All you have to do is plug in the value 40 for each x

f(x)=0.004x^3-0.12x^2+5.2x+12 

f(x)=.004(40)^3-0.12(40)^2+(5.2)(40)+12

256-192+208+12=284 is the height of the track when x=40