John buys game loot boxes for $5 each. The average value of items inside is $3.5.  He spends $40 on loot boxes. What is the average amount he lost?
Stream of thoughts:
12
He bought 40 / 5 = 8 boxes.

He loses an average of 5 - 3.

5 = $1.

50 per box.

So he loses an average of 1.

5 * 8 = $12.

.

The answer is 12