A bakery sells two types of cookies: chocolate chip and oatmeal. On Monday, the bakery sold 30 chocolate chip cookies and 20 oatmeal cookies for a total of $105.00. On Tuesday, they sold 30 chocolate chip cookies and 15 oatmeal cookies for a total of $90.00. If $c$ represents the price of a chocolate chip cookie and $o$ represents the price of an oatmeal cookie, what is the price of one oatmeal cookie?