The decomposition of the parallelogram into triangle then into a rectangle is shown below
The measurement we need to calculate the area is the length and the width of the rectangle; 15 feet and 10 feet
Area = 15 × 10 = 150 feet²

now, a line perpendicular to that one, will have a "negative reciprocal" slope, thus
2x^2+8xy+8y^2
2(x^2+4xy+4y^2)