Can u plz help with calculating

In Suppose a simple economy with only consumption, investment and government. Further suppose Income (Y) = R1000, the marginal propensity to consume (b) = 0.8, autonomous consumption (a) = R100, Investment (1) = R80. Government consumption (G) = R100 and the tax rate (t) = 0.1. a. Calculate the size of the expenditure multiplier. b. Calculate the size of the tax multiplier. Suppose investment (I) increases by R100, calculate the new income level following the increase in investment. Also use the appropriate graph to explain the effect of the increase in investment on income. Suppose the tax rate on income (t) increases from 0.1 to 0.15, what will be the value of equilibrium income following the increase in the tax rate? Also use the appropriate graph to explain the effect of the increase in the tax rate on income