To find the equilibrium national income, we need to set up the national income identity:
\[
Y = C + I + G + (X - M)
\]
### Step 1: Calculate disposable income (Yd)
Disposable income (Yd) is given by:
\[
Y_d = Y - T
\]
where T is tax revenue, given by:
\[
T = 0.3Y
\]
So:
\[
Y_d = Y - 0.3Y = 0.7Y
\]
### Step 2: Substitute Yd into the consumption function (C)
The consumption function is given by:
\[
C = 50 + 0.8Y_d
\]
Substituting for