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<p>In the image, there is a quadrilateral within the rectangle that has x as one of its angles. To find a+b in terms of x, an equation can be created that involves the sum of the angles of the quadrilateral equaling to 360. The northeast angle of the figure is obviously 90, but the two obtuse angles are equal to 180-a and 180-b because they’re on straight lines. Since all of the angles of the quadrilateral are now known, the equation 90+180-a+180-b+x=360 can be used to find a+b, which is equal to 90+x.</p>