Stream of consciousness rationale: The school needs to buy 30 - 12 = 18 robes. So the school will spend 18 x $2 = $36.
The question and answer pair are described below.
Q: A school choir needs robes for each of its 30 singers. Currently, the school has only 12 robes so they decided to buy the rest. If each robe costs $2, how much will the school spend?
A: 36