AMC 8 2007 Problem 7

The average age of $5$ people in a room is $30$ years. An $18$-year-old person leaves the room. What is the average age of the four remaining people? $\mathrm{(A)}\ 25 \mathrm{(B)}\ 26 \mathrm{(C)}\ 29 \mathrm{(D)}\ 33 \mathrm{(E)}\ 36$