The Keynesian model is for an open economy with a government sector. 

4.4 Explain the marginal propensity to consume for this model by incorporating the provided information in your answer. (2) 
4.5 Calculate the multiplier for this economy (3)                    

See explanation.

Step-by-step explanation

Aggregate consumption C is shown as:

C = Co + cYd, where

Co is autonomous consumption,

Yd is disposable income which is Y -Taxes

c is the marginal propensity to consume

The C function, is therefore, composed of two components---

autonomous ( not related to income) and induced ( related to income).

C increases as domestic income rises and falls if Y declines.

The marginal propensity to consume  in  graph, is shown by the slope of C function.

MPC = Change in consumption/Change in disposable income

MPS = marginal propensity to save = 1-MPC.

The expenditures multiplier = 1/(1-MPC).

Thus, if MPC = 0.75, multiplier = 1/(1-0.75) = 1/0.25 = 4.

That means that any expenditure like in I or G will create 4 of income or Y.

Higher the MPC, the bigger the multiplier.