Question

The number of books read by a mathematician 2 years after he turned 25 is given by the polynomial

Answer 1

Evaluating a function means to plug the required value, substituting every x occurrence with that value.

So, you have

$f(x)=3x^2+80x \implies f(2) = 3\cdot 2^2+80\cdot 2 = 3\cdot 4 + 160 = 12+160=172$