Alicia runs a small business mowing yards in the summer. For every yard she mows, she earns $40. However, she spends part of this money on gasoline for her lawnmower. Each gallon of gasoline costs $3. Write an expression for the amount of money that Alicia earns in a day, where y is the number of yards she mows and g is the number of gallons of gasoline she buys.