Question 1111469
 Bobby is 3 years older than Chris
b = c + 3
or
b - c = 3
 last year the sum of their age was 39 how old each now
(b-1) + (c-1) = 39
b + c - 2 + 39
b + c = 41
:
Use elimination
b - c = 3
b + c = 41
-------------addition eliminates c, find b
2b = 44
b = 22 yrs is Bob's age
then obviously
c = 19 yrs is Chris's age
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Check
"last year the sum of their age was 39"
(22-1) + (19-1) = 39