Find equilibrium GDP using the following macroeconomic model (where the numbers, with the exception of the MPC, represent billions of dollars).
1. C = 1,500 + 0.75Y ....................... Consumption function
2. I = 1,250 .................................. Planned investment function
3. G = 1,250 ................................. Government purchases function
4. NX = - 250 ............................... Net export function
5. Y = C + I + G + NX .................... Equilibrium condition