Let the sides of the triangle be $$3x, 4x and 5x$$ $$ecause$$ $$(3x)^2+(4x)^2 = 25x^2 = (5x)^2$$ => These are the sides of a right angled triangle and since $$5x$$ is the longest side, it will be hypotenuse Area of triangle = $$frac{1}{2} * 3x * 4x$$ = 7776 => $$x^2$$ = 1296 => $$x = sqrt{1296}$$ = 36 => Perimeter of triangle = $$3x + 4x + 5x$$ = $$12x$$ = 12*36 = 432 cm