Ans: A
The sum of the percentage of overweight girls and the percentage overweight boys is equal to the percentage of overweight students. Then, we have
$\begin{array}{rcl}
60\% \times 45\% + (1-60\%) \times x\% & = & 33\% \\
0.27 + 0.4 \times \dfrac{x}{100} & = & 0.33 \\
0.4 \times \dfrac{x}{100} & = & 0.06 \\
\dfrac{x}{100} & = & 0.15 \\
x & = & 15
\end{array}$
