By how much will GDP change if firms decrease their investment by $-8 billion and the MPC is 0.9? If the MPC is 0.8?

Change in GDP with MPC of 0.9 = $ billion
Change in GDP with MPC of 0.8 = $ billion (Instructions: round this answer to the closest billion. For example, 82,282,282,282 would be rounded to 82 billion.)

I've been really confused on how MPC and MPS work with investment. If you can show the formulas and steps, that would be great. Thank you!

Question

By how much will GDP change if firms decrease their investment by $-8 billion and the MPC is 0.9?  If the MPC is 0.8?

Change in GDP with MPC of 0.9 = $ billion
Change in GDP with MPC of 0.8 = $ billion (Instructions: round this answer to the closest billion. For example, 82,282,282,282 would be rounded to 82 billion.)

I've been really confused on how MPC and MPS work with investment. If you can show the formulas and steps, that would be great. Thank you!