Verified Answer :

Let, Jason = J and M = Megan

M = J(1 + 1/4) 

So putting 6 where J is and solving:
M = 6(1 + 1/4)
M= 7.5

When Jason runs 6 miles Megan runs 7.5

M=1.25J
M=1.25
6
M=7.5 miles