(a) a unique solution
The given equations are of the form a1x + b1y + c1 = 0 and a2x + b2y + c2 = 0, where
a1 = 4, b1 = - 5, c1 = - 20 and a2 = 3, b2 = 5 and c2 = - 15
∴ , and
∴ These graph lines will intersect at a unique point, when .
Hence, the given system has a unique solution.