Find the value of X

please help

An architect is designing a water fountain for a park she uses the given function to model the water jet flowing from the fountain nozzles where h(x) gives the height of the water jugs in feet x feet from the starting point h(x)=-1/20x+x+15

If f(x)=-x^2+6x-1 and g(x)=3x^2-4x-1,find(f+g)(x)

What does independent variable and dependent variable mean in math?