Question

Julia is five years older than her sister Babs, and their ages add up to 31. How old is Babs?

Answer 1

Attached solution plus work.

Answer 2

Julia is X+5

x+x+5=31

Now we just solve the equation 

2x=31-5
x=26/2
x=13 years old (Babs' age)

and we know that julia is 5 years older this gives us the conclusion that. 

13+18=31