if 10 ppl need 110 days to construct the building, a person does 1/1100 th work per day.
5 days of rain, implies that they worked only 55 day in 60 days. until then: 55 * 10 / 1100 = 0.5

later he hired 6 more workers totaling 16. since they had done 50% of the work, we can say that to finish it they took: (16/1100)x = 0.5
Solve for x and it comes up 34.7 ~~ 35 days. they actually worked 35 days.

since they had done the job in 100 days and 40 days were left, we can conclude that it rained 5 days.

OA?

As the question states that the contractor with his group of 10 workers could get a work done in 110 days without any rain

Further it is given that it rained on the 61st day for 5 days.
As such the work for 60 days was completed.

Work left equivalent to 50 days. contractor increased the workforce by 6 to 16.
this workforce could have done the work of 50 days for 10 workers in 50*10/16= 31.25 days
Since this is working days we are talking about therefore the days will be rounded up to 32.

As such the work should have been completed in
60(work done previously) + 32 (days it should have taken 16 men to complete the work) + 5 (days given that it rained) =97
But it is stated in the question that the work was completed in the 100 days therefore it must have rained for 3 more days afterwards.

Therefore total days it had rained after day 60 is 5+3=8

Answer E.