Reconstruct a question, answer pair from this explanation: He started with 2 * 4 = 8 trees. He plants trees for 15 - 10 = 5 years. So he planted 5 * 4 = 20 trees. So he had 20 + 8 = 28 trees. After doubling them he had 28 * 2 = 56 trees.
Q:Jim has 2 rows of 4 trees to start. When he turns 10 he decides to plant a new row of trees every year on his birthday. On his 15th birthday after he doubles the number of trees he has. How many trees does he have?
A:56