A rectangular brick platform is built in horizontal courses. The first (bottom) course contains 30 bricks. Each course above it contains exactly 2 fewer bricks than the course just below it. The platform contains a total of 240 bricks.
(i) Prove that the number of bricks in successive courses forms an arithmetic progression. State its first term and common difference.
(ii) Form an equation for the total number of bricks in n courses and hence determine the number of courses used in the platform.
(iii) How many bricks are there in the topmost course? Comment on the reasonableness of this value for practical construction.