can you help me with these and please explain how you got your answer, i need to fully understand them

\f1 3 MC Qu. 32-19 (Algal If investment decreases by... If investment decreases by $20 billion and the economy's MPC is 0.5, the aggregate demand curve will shift points Multiple Choice eBook O leftward by $40 billion at each price level. rightward by $20 billion at each price level. leftward by $20 billion at each price level. 0 rightward by $40 billion at each price level. 1 8 MC Qu. 32-18 (Algal If investment increases by... If investment increases by $15 billion and the economy's MPC is 0.8, the aggregate demand curve will shift 5 polnts Multiple Choice eBook O rightward by $?5 billion at each price level. rightward by $15 billion at each price level. leftward by $30 billion at each price level. 0 leftward by $?5 billion at each price level.