IMAS 2016 — Middle Primary Grades 3–4 — Round 2 Question 9

Refer to the diagram below, where 9 black bricks and 4 white bricks are arranged alternately such that it will form a figure in which there are 5 bricks on its diagonals, and all the outer bricks are black.



Using the similar pattern stated above, if we want to form figures in which there are 7 bricks on its diagonals, how many black bricks are required?