Answer:
The length of a is 36 mm.
Explanation:
Similar rectangles have the same shape, but can have different sizes. The ratio of the lengths of corresponding sides of similar rectangles is always the same.
Given that b = 18 mm, c = 24 mm, and d = 36 mm, the ratio of the lengths of corresponding sides of the two rectangles is c/d = 24/36 = 2/3.
So, the length of a is equal to b * (c/d) = 18 * (2/3) = 36 mm.