First: Recognize that (f o g)(x) is the "composition" of two functions, where g(x) serves as the input to f(x). We are given f(x) = 2x+3 and g(x) = x+5. You could find g(3) right now: it is g(3) = 3+5 = 8. Use this 8 as the input to f(x): f(8) = 2(8)+3 = 19.
