In 2000 4½ ft. In 2005 15¾ ft. rate of growth measured in ft per year?

Question

In 2000 Jim planted a tree that was 4½ feet tall. In 2005 the tree was 15¾ feet tall. Assuming the growth of the tree is linear, what was the rate of growth of the tree measured in feet per year? Doesn't need to be worked out, I just need the answer. I've been trying for days to answer this but I still have no idea. Please help?

Answer 1

delta yeer=2005-2000=5

delft ft =(15 & 3/4) - (4 & 1/2)

=15.75 -4.5

=11.25

ft/yeers=11.25/5=2.25 ft/yeer