Explanation:
This is called a nested function. Remember, math is a language.
We define a function where x is whatever we want it to be, f(x) = g(x) +10
but we have yet another function inside and itvs defined as g(x) = 3x - 18
if we were to write it out, it woukd be
f(x) = (3x - 18) + 10