You get $50 from your mom and $50 from your dad. You buy a shirt for $97 and get $3 change.
You give $1 back to your mom and $1 back to your dad and keep $1 for yourself. Now you owe your mom and dad $49 dollars each.
So sum it up, $49 x 2 = $98 + the $1 you kept = $99.