Help, please i really need help with this

Question

There are white, blue, and red boats in a marina. Two-thirds of the boats in the marina are white, 4/7

 of the remaining boats are blue, and the rest are red. If there are 15 red boats, how many boats are in the marina?

Answer 1

2/3 + 4/7)(1/3) = 14/21 + 4/21 = 18/21 = 6/7

15 are 1/7 of the boats

7 x 15 = 105 total boats in the marina

15 red

2/3 x 105 = 70 white

20 blue