Joel has twice as many cds as Mary has. Subtracting 7 from the number of cds Joel has and dividing by 3 equals the number of cds Blake has. If Blake has 25 cds, how many cds does Mary have?

mary's cds --- x

joel has ------ 2x
blake ------( 2x-7)/3

(2x-7)/3 = 25
2x-7 = 75
2x=82
x = 41

mary has 41
joel has 82
blake has 25