Joel has twice as many CDs as Mariella 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 Mariella have?

J = number of cd's joel has

m = number of cd's mariella has

b = number of cd's blake has

from problem statement, develop equations:

j = 2m

b = (j - 7) / 3 = 25

m = ?

solve for m

b = 25 = (j - 7) / 3

25 = (j - 7) / 3

25*3 = j - 7

75 + 7 = j

j = 82

j = 2m = 82

m = 82/2

m = 41

thus

mariella has 41 cd's

joel has 82 cd's

blake has 25 cd's