Write as an equation and solve
John is 4 years older than Becky, and John's
and Becky's combined ages is 58.
How old are Becky and John?
There are two equations here.
John's age is J, Becky's age is B
1) J = B + 4 or J - B = 4
2) J + B = 58
By adding the two equations, we eliminate
Becky's age from consideration, leaving us
with an equation that will give us John's age.
J + B = 58
+ (J - B = 4)
-------------------
2J = 62
J = 31
Use that to solve for Becky's age.
J = B + 4
31 = B + 4
31 - 4 = B
B = 27
John is 31, Becky is 27