Jack collected 360 ship models. 40% of them were made by him. If Jack donated 25% of models which he made and
donated 50% of models he bought, how many fewer models
made by himself were donated than those he bought?
fewer models donated made than bought

8.75

how-to:

first, we need to find what we have to work with.

since i know that we have 7 (years) and 0.8 (inches), we can use these to solve and find the equation!

secondly, what you want to do, is see that we need to know how much growth out of the 0.8 inches he got in only 1 year, instead of 7 years.

let's try to divide.

7 ÷ 0.8 = 8.75