Explanation:

Let the required number of days be x.

Then,Less pumps, More days(Indirect Proportion)

Less weight, Less days(Direct Proportion)

More hours / day, Less days(Indirect Proportion)

Pumps 16 : 18} : : 10 : x

Weight 2170 : 1736} :: 10 : x

Hours / Day 9 : 7} : : 10 : x

(16 * 2170 * 9 * x) = (18 * 1736 * 7 * 10)

 x = 18∗1736∗7∗10/16∗2170∗9 = 7.

Hence, the option 2 is the correct answer.