Answer:$20 = Charlie, $60 = Josh, $10 = Melissa
Explanation:
M+C+J=90 = Melissa, Charlie, and Josh have a total of $90 in their wallets
J=3C = Josh has 3 times what Charlie has
M=C-10 = Melissa has $10 less than Charlie.
Therefore
M+C+J=90
(C-10) + C + 3C=90
5C-10=90
5C=100
C=20 = Charlie
J=3C = 60 = Josh
M=C-10 = 10 = Melissa