Explanation:
Calculate the the total number of the boxes. We can calculate it by counting number of the rows and the number of the columns and then multiplying it.
Total number of rows = 10
Total number of columns = 10
Total boxes = 100
Shaded boxes = 72
We calculate %age by,
=> Selected boxes/Total boxes x 100
=> 72/100 x 100
=> 72%
Hope it helps :)