Question

The school is having a bake sale and the pep squad is selling cookies. On one ticket they sold four chocolate chip cookies and six oatmeal cookies for $30. On another ticket they sold four chocolate chip cookies and three oatmeal cookies for $21.

Which system of equations below can be used to determine the price of a chocolate chip cookie and the price of an oatmeal cookie?

Let x represent the cost of a chocolate chip cookie, and let y represent the cost of an oatmeal cookie.

8x + 9y = 51
8x - 9y = 51

4x + 6y = 30
4x + 3y = 21

4x + 4y = 30
6x + 3y = 21