The sides of the triangle are in the ratio 5:6:7 and its perimeter is 720cm. The length of the longest side is?  Choose the correct choice from the following answers.
A) 150 cm B) 200 cm C) 162 cm D) 220 cm E) 280 cm

Rationale: ratio of sides = 5 : 6 : 7 largest side = 720 * 7 / 18 = 280 cm answer is e
Answer: E