Answer: 90cm
Step-by-step explanation: 2x, 3x, and 4x is what your dealing with and you know the longest side (4x) is 20cm longer than the shortest side(2x) which means 4x-2x = 20 because of the difference. Solved is 2x = 20 and X equals 10 and since this is a ratio the x values are the same so all sides equals 2(10)+3(10)+4(10)= 90