Final answer:
To determine the number of regular and deluxe car washes sold to make a total of $1890, we use the equation 9x + 15y = 1890, where x is the number of regular washes and y is the number of deluxe washes. More information is needed to find a unique solution.
Step-by-step explanation:
To find out how many of each type of car wash could have been sold to make a total of $1890, we can set up a system of equations. Let the variable x represent the number of regular car washes sold at $9 each, and the variable y represent the number of deluxe car washes sold at $15 each.
The total amount made from the car washes is given by the equation:
9x + 15y = 1890
This equation represents the total revenue generated, which is the sum of $9 times the number of regular washes plus $15 times the number of deluxe washes, equaling $1890.
To solve this equation, more information is needed such as the total number of car washes sold. Without that, there are infinitely many solutions to this equation. However, if we had that information, we could represent it with another equation and solve the system of equations using substitution or elimination methods.