The graph of the revenue function is a parabola opening downward. The maximum occurs at the vertex. The x-coordinate of the vertex of a parabola with equation y = Ax2+Bx+C is x = -B/(2A).
So, for the given equation, the x-coordinate of the vertex is x = -48/(2(-3)) = 8
Therefore, to maximize revenue, sell 8 supercomputers
Maximum Revenue = R(8) = 48(8) - 3(8)2
= $192,000,000