9x^2 - 42x + 49 is a perfect square trinomial. It factors to (3x - 7)^2 If the area is 64m^2 set this equal to the factors and solve. (3x - 7)^2 = 64 Take the square root of both sides. 3x - 7 = + - 8 3x - 7 = 8 3x - 7 = - 8 Add 7 to both sides. 3x = 15 3x = - 1 Divide both sides by 3. x = 5 x = -1/3 x cannot be -1/3 because it would make the length negative. The answer is x= 5
