He spent $4.40 on apples, and $7.20 on bannans. If you add it you get $11.6, meaning he spent $4.90 on plums (16.5 - 11.6 = 4.9). Then you have to divide by 3 to get the per pound since there were 3 plums. You will get a repeating decimal (1.633) so you would round it to 1.63.
Plums cost $1.63 per pound.
