I assume the question is about perimeter rather than premeter. A perimeter is a measure of closed shapes and, unfortunately, two measures do not define a closed shape. It cannot be a polygon because a polygon must have at least three sides and if it is not a polygon there is not enough information to ascertain the shape.
20 cm
18/24 = 0.75 so 75 %
18+24=42
18 is 75% of 24.
fraction = 18/24 or 3/4
-42
18+18+18+19+23+23+24+24=167
19
18 multiplied by 24 is 432.
18 is 24% of 75
18
lcm for 18 and 24 is 72