Write an expression to represent the area of the shaded region in standard form

To determine what the area of the shaded region is, simply find the area of the large rectangle and subtract the product from the smaller one.

Since they are polynomials. Multiply one binomial to the other and first obtain the product, before subtracting the product of the smaller rectangle.

(5x + 2)(3x - 1) - (x)(x + 7)

15x^2 - 5x + 6x - 2 - x^2 - 7

14x^2 + x - 9.

I believe this would be the solution in standard form.