帮我解答一个英语应用题,谢谢~~

帮我解答一个英语应用题,谢谢~~
Several years ago,I planted a 7-foot tree in my yard.The tree has grown 3 feet each year,and last year it was four times the original height.How tall is the tree now,and how long ago did I plant it?
最好把这到题的答案、中文意思写出来~
（是绝对鄙视,杜绝用翻译器的人的!）