Question 984764
f(1) means "the value of the function f(x) when x=1" 

To solve (which you are not asked to do by the way), you evaluate the function f(x) where x=1. 
So replace x with the number 1 everywhere in the function f(x)
{{{f(x) = 2x + 1}}}
{{{f(1) = 2(1) + 1}}}
{{{f(1) = 3}}}