The school is having a bake sale and the pep squad is selling cookies. On one ticket they sold four chocolate chip cookies and five oatmeal cookies for $31. On another ticket they sold five chocolate chip cookies and two oatmeal cookies for $26. 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.