Tommy put some money in his pocket and went to the store. After paying $12 for a kite, he had 3/7 of his money left. How much money did Tommy have left?
M - 12 = (3/7)M
M - (3/7)M = 12
(4/7)M = 12
M = 12 (7/4) = $21 is what he started with
He has 21 - 12 = $9 left
let's call the money he initally had = $x
when he removes $12 from $x he had 3/7 of $x left
$x - $12 = 3/7 of $x
($x - $12) = $3x/7
7 ($x - 12) = $3x
$7x - $84 = $3x
$7x - $3x = $84
$4x = $84
$x = 21
Therefore he initially had $21.
$21 - (how much spent) = (what's left)
$21 - $12 = $9.
$9 was left