Find an algebraic expression that represents the area of the shaded region

taking a peek at the outer rectangle, it has a length of 4x - 3 and a width of "x", so it has an area of (4x-3)(x).

now, the tiny square inside the larger rectangle, has an area of (x-4)(x-4), if we subtract the area of the square inside from the area of the larger rectangle, what's leftover is just the shaded area.