Question 690739
Let s = sisters age
and y = your age

then, "My sister is 5 years older than I" ==> s = y + 5      Eq (1)
and "the sum of our ages equals 35" ==> s + y = 35     Eq (2)

Substituting s = y + 5 into Eq (2) gives:
  (y + 5) + y = 35
  2y + 5 =35
  2y = 30
  y = 15

Substituting y = 15 into Eq (1) gives:
  s = 15 + 5
  s = 20

So your age is 15, your sisters age is 20