length = 3x + 6xPerimeter = 84 cmA9B8C18D10 Step-by-Step SolutionLet breadth = x, length = 3x+6. Perimeter = 2(x+3x+6)=84, so 2(4x+6)=84,8x+12=84,8x=72,x=9.Answer: A) 9