see at first 100% work can be done in 100 days means 1% work in a man day.
now writing code in assembly language is 10 times harder means 10 times more time consuming.
also converting existing code form c++ is 4 times easier i.e less time consuming so overall by this scenario we can say 100% work can be done in 100*10/4 man days = 250 days.
So, 1% work will be done in 2.5 days.
NOW,99% work in C++ + 1% rewriting code will take = 99*1 + 1*2.5= 101.5 man days.
but we are given 13 days to complete so 101.5/13 = 8 programmer we need.
Ans-C