The eighth grade class at Lincoln Middle School has $93$ students. Each student takes a math class or a foreign language class or both. There are $70$ eighth graders taking a math class, and there are $54$ eighth graders taking a foreign language class. How many eighth graders take only a math class and not a foreign language class?
$\textbf{(A) }16\qquad\textbf{(B) }53\qquad\textbf{(C) }31\qquad\textbf{(D) }39\qquad\textbf{(E) }70$
Let $x$ be the number of students taking both a math and a foreign language class.
By P-I-E, we get $70 + 54 - x$ = $93$. 
Solving gives us $x = 31$.
But we want the number of students taking only a math class,
which is $70 - 31 = 39$.
$\boxed{\textbf{(D)}\ 39}$
~phoenixfire