The converse of the same side exterior angles theorem states that <em>when two same side exterior angles are supplementary, the two lines they are on are parallel</em>.
So that means that<em> 5x + 9 and 3x + 11 are supplementary</em>.
Use the law of cosines. Let be the distance between the docks, which forms a third leg of a triangle for which the angle opposite it has measure 45 degrees. The other two legs have lengths 400 ft and 500 ft. So