Suppose the closed economy is in long-run equilibrium. Advances in technology shift the

long-run aggregate-supply curve $80 billion to the right. Optimistic investors have shifted the

aggregate-demand curve $150 billion to the right. In order to stabilize the price level at its

original value, the government wants to reduce its spending. If the crowding-out effect is always

half of the multiplier effect, and if the MPC equals 0.75, by how much must the government cut

its spending?

A : $4 billion

B : $40 billion

C : $75 billion

D : $150 billion

I know the answer is B, but I'm looking for the steps to get the answer.