Well between year 1 and 2, income increased by 150 but consumption increased by 90 so the marginal propensity to consume is 90/150=3/5. Therefore the MPS is 2/5 and the multiplier is 1/MPS=5/2
So an increase in investment by $40bn will have a $40x5/2 increase in national income -> $100bn increase -> $300bn (C)