a) Find IS Curve Step 1: The goods market equilibrium condition is $Y = C + I + G$. Substitute the given equations for $C$, $I$, $T$, and $G$: $$C = 1500 + 0.75(Y-T)$$ $$I = 1000 - 100r$$ $$T = 0$$ $$G = 0$$ $$Y = [1500 + 0.75(Y-0)] + [1000 - 100r] + 0$$ $$Y = 1500 + 0.75Y + 1000 - 100r$$ Step 2: Combine constant terms and rearrange to solve for $Y$: $$Y = 2500 + 0.75Y - 100r$$ $$Y - 0.75Y = 2500 - 100r$$ $$0.25Y = 2500 - 100r$$ $$Y = \frac{2500}{0.25} - \frac{100}{0.25}r$$ $$Y = 10000 - 400r$$ The IS curve is $\boxed{Y = 10000 - 400r}$. b) Find LM Curve Step 1: The money market equilibrium condition is $M_s = M_d$. Substitute the given equations for Money Supply ($M_s$) and Money Demand ($M_d$): $$M_s = 2000$$ $$M_d = 0.5Y - 200r$$ $$2000 = 0.5Y - 200r$$ Step 2: Rearrange the equation to solve for $Y$: $$0.5Y = 2000 + 200r$$ $$Y = \frac{2000}{0.5} + \frac{200}{0.5}r$$ $$Y = 4000 + 400r$$ The LM curve is $\boxed{Y = 4000 + 400r}$. c) Find equilibrium level of $Y$ and $r$ Step 1: Set the IS curve equation equal to the LM curve equation to find the equilibrium interest rate ($r$): $$10000 - 400r = 4000 + 400r$$ Step 2: Solve for $r$: $$10000 - 4000 = 400r + 400r$$ $$6000 = 800r$$ $$r = \frac{6000}{800}$$ $$r = \frac{60}{8}$$ $$r = 7.5$$ Step 3: Substitute the equilibrium value of $r$ into either the IS or LM equation to find the equilibrium output ($Y$). Using the LM equation: $$Y = 4000 + 400r$$ $$Y = 4000 + 400(7.5)$$ $$Y = 4000 + 3000$$ $$Y = 7000$$ The equilibrium level of $Y$ is $\boxed{7000}$ and the equilibrium level of $r$ is $\boxed{7.5}$.