Can someone please explain how to find the answer? My old teacher didn’t do it this way and I’m lost :/

What is f(3) for the quadratic function f(x)= 2x^2+ + x - 12

The physical fitness of an athlete is often measured by how much oxygen the athlete takes in (which is recorded in milliliters per kilogram, ml/kg). the mean maximum oxygen uptake for elite athletes has been found to be 60 with a standard deviation of 7.2. assume that the distribution is approximately normal.

F(x)=x/2-2 and g(x)=2x^2+x-3 find (f+g)(x)