First, let us find out how many miles the hikers travel per day.
They walk at a rate of two mph for eight hours each day which means that they travel 16 miles per day (8x2).
Because the total distance of the great wall is 3948 miles to find out the amount of time needed...
3948/16 = 246.75 days (which is greater than 3 months)
answer: They can't cover the entire distance in three months.