When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a constant amount each year for the next 6 years. At the end of the 6th year, the tree was 1/4 taller than it was at the end of the 4th year. By how many feet did the height of the tree increase each year?  Choose the correct choice from the following answers:  A) 1  B) 2 / 5  C) 1 / 2  D) 2 / 3  E) 6 / 5

Rationale: "say , the tree grows by x feet every year . then , 4 + 6 x = ( 1 + 1 / 4 ) ( 4 + 4 x ) or , x = 1 answer a"
Answer: A