John is filling a bathtub that is 18 inches deep. he notices that it takes two minutes to fill the tub with three inches of water. he estimates that it will take ten more minutes for the water to reach the top of the tub if he continues at the same rate. is he correct?

Depth of the bathtub = 18 inches
Time taken to fill 3 inches of the bathtub = 2 minutes
Then
The amount of depth needed to fill with water = (18-3) inches
                                                                         = 15 inches
Time required to fill 15 inches of the bathtub = (15*2)/3 minutes
                                                                       = 30/3 minutes
                                                                       = 10 minutes
So John is correct in thinking that it will take 10 more minutes for the water to reach the top of the tub if he continues at the same rate.