Question 1005425
Call their ages NOW, f and s.  Then we have
f - 5 = 7(s - 5)  and
f + 5 = 3(s + 5)
Solve the first one for f and substitute that into the second equation...
f = 7(s - 5) + 5 = 7s - 35 + 5 = 7s - 30
and now substituting
7s - 30 + 5 = 3(s + 5)
7s - 25 = 3s + 15
4s - 25 = 15
4s = 40
s = 10
f is then 40.