Solve the Problem $f ( x ) = 6.75 \sqrt { x } + 12$

Solve the problem.
-The function $f ( x ) = 6.75 \sqrt { x } + 12$ models the amount, $f ( x )$ , in billions of dollars of new student loans $x$ years after 1993. According to the model, in what year is the amount loaned expected to reach $\$ 45.75$ billion?

A) 2018
B) 2021
C) 2023
D) 2022