Question #cf87c

1 Answer
Nov 14, 2016

Jason is 15

Explanation:

Let
XXXJ be Jason's age
XXXS be Jason's sister's age
XXXM be Jason's mother's age

We are told
[1]XXXJ=S+6
[2]XXXM=J+S+15
[3]XXXM=39

Combining [2] and [3], we have
[4]XXXJ+S+15=39

Using [1], we can substitute S+6 for J in [4]
[5]XXXS+6+S+15=39

Simplifying
[6]XXX2S+21=39

[7]XXX2S=18

[8]XXXS=9

Using [8], we can substituting 9 for S in [1]
[9]XXXJ=9+6=15