Answer:
He needs 1 more fish tank.
Explanation:
18 / 3 = X (X equals the number of fish tanks he needs)
2 + 3 = 5 fish tanks
5 x 3 = 15 fish
18 -15 = 3
Since 5 fish tanks can hold 15 fish he will need 6 fish tanks to hold his 18 fish. He will need 1 more fish tank.