Need a diagram and a formula

Question

a page in a book is 10 inches wide by 12 inches tall. there is a 1 inch margin around the page that cannot be used for pictures. the space between the picture is at least 1/2 inch. how many 3 inch tall pictures can you fit on the page in one column.

Answer 1

3 + 1/2 + 3 + 1/2 + 3 = 10

 

10 + 1/2 + 3 = 13.5  

 

Three pictures will fit.  Four pictures will take up too much space.