a) The diagonals of a square are perpendicular forming 4 right triangles.
a² + a² = 90²
2a² = 90²
a² = 4050
a rounds to 64 feet.

b) The angle labeled b is an acute angle of an isosceles right triangle. These acute angles are equal in measure.
b + b + 90 = 180
2b = 90
b = 45º