The input-output characteristics of two generating units are as follows:
F₁ = 0.001PG₁² + 0.5P + 3 Btu/h
F₂ = 0.002PG₂² + 0.3P + 5 Btu/h

The power output limits of the two units are:
100 ≤ PG₁ ≤ 280 MW
150 ≤ PG₂ ≤ 300 MW

Determine the economic operation point for these two units when delivering a total of 500 MW power demand.