A flight school operates 5 airplanes of the different types. All airplanes are outdated and require some modifications. The school has $33,000 available in the budget for the airplane modification this year which cannot cover all airplanes. An aviation engineer came up with the plan to update all airplanes. Some details of the plan are shown in the following table:

Airplane Modification cost Present worth of benefits

1 $6,000 $54,000

2 $9,000 $56,000

3 $7,000 $55,000

4 $11,000 $59,000

5 $8,000 $60,000

Which airplane modification does the school have to postpone until next year?

Possible Answers

A. 3

B. 1

C.5

D. 4

E. 2

with explanation please