The volume is equal to 134.041
SinA=8/17, so arcsin(8/17) is your angle of A (around 49 degrees). 90-A is your angle for B
Now, recalling that for 1 yard, there are 3 feet, therefore

and keeping in mind that, there are 4840 yd² in 1 acre, then
With these transversals across parallel lines the angles are either congruent or supplementary (adding to 180) and its pretty easy to figure out which is which, obtuse verse acute in the figure.
Each yellow circle indicates x and the path to the next square. So for example the Start has alternate interior angles, which are congruent, so x is 141 degrees.
He would have 21 before he bought the 10 stamp because 31-10=21