A homework question on Marginal Propensity to consume. I can't find the right answer?

Question

Assuming that the MPC is .75, equal $10 billion increases in government spending and tax collections will:

a. leave the equilibrium GDP unchanged
b. increase the equilibrium GDP by $ 10 billion
c. increase the equilibrium GDP by $ 2.5 billion
d. reduce the equilibrium GDP by $ 10 billion

I cant find the right answer, I thought that the answer was $40 billion, found by:

10 billion x (1/1-.75)
10 billion x (1/.25)
10 billion x (4)
40 billion is not an option, am I missing something?

Answer 1

c. increase the equilibrium GDP by $ 2.5 billion

Consumers spend 75 cents on every $1 they have. The government takes $10 billion away from them so they spend $7.5 billion less. The government spends all of the $10 billion.

change to GDP is $10B - 7.5B = $2.5 billion