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 1/7 taller than it was at the end of the 4th year. By how many feet did the height of the tree increase each year? Options:  A) 3/10  B) 2/5  C) 1/2  D) 2/3  E) 6/5
Say, the tree grows by x feet every year.   Then, 4 + 6x = (1+1/7)(4+4x)   or, x = 2/5   Answer 2/5
<result>B</result>
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 1/7 taller than it was at the end of the 4th year. By how many feet did the height of the tree increase each year?