Answer: it will take 0.25 years for these trees to be the same height.
Explanation:
Let x represent the number of years that it will take these trees to be the same height.
Type A tree is 5 feet tall and grows at a rate of 13 inches per year. This means that the total height of Type A tree after x years would be
13x + 5
Type B tree is 3 feet tall and grows at a rate of 21 inches per year. This means that the total height of Type B tree after x years would be
21x + 3
For both trees to be of the same height, the number of years would be
13x + 5 = 21x + 3
21x - 13x = 5 - 3
8x = 2
x = 2/8 = 0.25