Perimeter of an object can be found using the general formula: P = 2W + 2L, where P = perimeter, W = width and L= length. Since both the width and perimeter of the window are given, we can plug these values into the formula to solve for the missing variable 'L': 112 = 2(21) + 2L, or 112 = 42 + 2L. We can then use inverse (opposite) operations to isolate the variable and solve. Whatever we do to one side of the equation, we do to the other. We will start by subtracting 42 from each side: 112 - 42 = 42 - 42 + 2L or 70 = 2L. Next, we divide both sides by 2 to solve for L: 70/2 = 2L/2 or L = 35. So, the final length of the window is 35 inches.
