Andrea's fish tank holds 30 gallons of water. Andrea estimates that every inch of a fish's length requires a gallon of water. She wants to purchase some corydoras that are 2 inches long, angelfish that are 5 inches long, and fancy guppies that are 3 inches long. Write an equation for the situation.
x + y + z = 30
2x + 5y + 3z = 300
x + y + z = 100
2x + 5y + 3z = 30