A reflection is the opposite direction so, if it's eight units to the left, the reflection will be eight units to the right, and we know the right is positive and left is negative.
1. The area of the full rectangle is 21 * 28 = 588. We will need this later.
Like you drew, there is an imaginary triangle missing. We can find the dimensions of it by subtracting from the given information. The shorter leg of it is 21 - 12 = 9, the longer leg is 28 - 14 = 14.
Now we find the area of the triangle. Area of a triangle is 1/2 * base * height. So 1/2 * 9 * 14 = 1/2 * 126 = 63.
Now we do the full area of 588 minus the area of the missing triangle piece.
588 - 63 = 525 ft²
2. Do the area of the rectangle and then this time add on the area of the triangle. 7 * 15 = 105. Area of the triangle = 1/2 * 2 * 7 = 1/2 * 14 = 7. 105 + 7 = 112 in²
