Olivia is painting a logo for a billboard and wants to use a combination of blue paint and red paint to completely cover a 5000 square foot billboard. A gallon of paint can cover 500 square feet. Red paint costs $20 per gallon and blue paint costs $30 per gallon. She only has $250 to spend. Write a system of inequalities that can be used to show all the possible combinations of paint that meet her goals.