First, assign a provision the value of 1. The purpose of this is to figure out exactly how many provisions the fort has.



225 people x 75 days x 1 provision/day = 75 x 225 people-provisions (There is a reason not to do the math right away)



Really, the first step can be skipped if you understand the problem because we are just going to reduce the days by 26 to 49:



225 people x 49 days x 1 provision/day = 49 x 225 people-provisions (Still not going to do the math)



With 50 people leaving (175 remaining), there will be a new number of days the fort can last. We will add 26 to that result to get the final answer (remember the question is asking for the total number of days).



49 x 225 people-provisions / 175 people/day = 49 x 225 / (7 x 25) = 7 x 9 or 63 days



26 + 63 = 89.



THE ANSWER IS E.

consider 225 person need 1 provision to stay.

so 225 people need total of 225*75 provision for 75 day.
but 225 people only stay for 26 day. So, provision consumed by them is 225*26.
Now the provision left is (225*75) - (225*26) = 225(75-26) = 225 * 49

now 175 people can consume this provision in [(225*49)/175] days = 63

so 26 days + 63 days = 89 days

hope this helps