Question 895821
M+6=3(S+6)
Distribute
M+6=3S+18
Subtract 6 from each side
M = 3S+12
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M-3 = 9(S-3)
Distribute
M-3=9s-27
Add 3 to each side
M = 9S-24
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Take the value of M from the first equation and substitute it for M in the second.
M = 9S-24
(3S+12)=9S-24
Subtract 3S from each side
12 = 6S-24
Add 24 to each side
36 = 6S
Divide each side by 6
S = 6
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If the son is 6 years old, then 3 years ago he was 3 years old.  At that time, his dad was 9x his age, or 27.  That was 3 years ago.  Now he's 30.
Son=6
Dad=30