[求助]一道Gmatprep

叮叮当当

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 1/5 taller than it was at the end of the 4th year. By how many feet did the height of the tree increase each year??

3/10

2/5

1/2

2/3  key

6/5

我做完的答案是4/7， 哪位能帮忙？？

先谢谢了。。

periodic

估计你看错题了

At the end of the 6th year, the tree was 1/5 taller than it was at the end of the 4th year.

设每年长X，方程式为

4+6X=(4+4X)* (1+1/5)