On wednesday 20 of the 25 students in a Math class took a test, and this average score was 85. On Thursday the other 5 students took the test and this average score was 90. What was the average score of the entire class ?

Question

$\begin{array}{1 1} (a)\; 80 \\ (b)\; 82 \\ (c)\; 84 \\ (d)\; 86\end{array}$