a.
Friday:
Saturday:
b.
Divide both sides by 30:
Simplify the fraction:
(It is impossible to solve for specific values for x and y as seen in part c, so I'm not sure what the question is asking to solve for.)
c.
Substitute x = (91-2y)/3 in that equation (which is Saturday's equation)
Hence, there is an infinite amount of solutions for x and y.