Because line s intersects line b, the angle opposite the given angle of (11x) must also be (11x) and the angle adjacent to (11x) must be 180-(11x) because those two angles together should equal 180, or the angle of a straight line. Next, we know that the sum of the angles of a triangle are 180 (think of 45, 45, 90 triangles for example). We know that the right angle is 90 degrees, which means the other two angles add up to the remaining 90. This means the angle not given in the right triangle will be 90-(7x). We also determined that this angle should equal (11x). So we could write out the equation (11x) = 90 - (7x). This can be rewritten as 90 = (11x) + (7x). We could then combine like terms to get 90 = 18x. Then divide both sides to solve for x and we would find that x = 5. Hope this helps and comment if you have any further questions. (:
