John is going to back to that is 18 inches deep he notices that it takes two minutes to fill the bathtub with 3 inches of water he estimates it will take 10 more minutes for the water to reach the top of the tub if he continues at the same rate is he correct

Yes,

Every 2 minutes = 3 inches of water, so that means every minute = 1.5 inches of water.

So in 10 minutes:

10 * (1.5) = 15 inches of water.

So in 10 minutes the tub will fill an additional 15 inches of water which is exactly how much you need to fill up the remaining tub (3+15 = 18)