the missing side is 7 (option C)
Explanation:
The triangles are similar triangles. This means the ratio of their corresponding sides are equal.
let the unknown = x
6m/18m = x/21m = 8m/24m
Picking any two ratios to find x:
6m/18m = x/21m
cross multiply:
x(18) = 6(21)
18x = 126
DIvide both sides by 18:
18x/18 = 126/18
x = 7m
Hence, the missing side is 7 (option C)
