JNU SSS 2014 Question 41: Keynesian cross and the multiplier

Suppose in economies $A$ and $B$ the aggregate value of output is $Y = C + G$, the sum of aggregate consumption and lump-sum government expenditures. The government imposes only lump-sum direct taxes and suppose $T$ denotes the aggregate value of such taxes collected by the government. $C = a + bY_d$, where $a$ is the value of autonomous consumption expenditures, $b$ is the constant marginal propensity to consume out of income and $Y_d$ is the aggregate value of disposable incomes in the economy. The value of $b$ is higher in $B$ than in $A$.

Suppose the value of $G - T$ is the same in both economies. Suppose that the value of $a$ is higher in economy $B$ than in economy $A$. In which economy will aggregate private saving be higher?