Ihave to find the length of the angle indicated for the trapezoid

That is not a trapezoid, it is a general quadrilateral.  All 2-dimensional, 4-sided figures have an internal angle sum of 360 (triangles are 180).  So if you assume angles P and Q are right, they are each equal to 90 degrees, for a total of 180.
Subtract: 360 - 180 = 180.  We know that S + R must equal 180.  If you subtract 180 - 65, you get 115, which is obtuse (greater than 90 degrees).  This matches the drawing as the unknown angle is clearly greater than 90.  So the answer is 115 degrees.

Yes you do, so £1973.09 - £1473.50 = £499.59 so tim overpaid £499.59 .hope this ; )