Merritt's Bakery sold one customer 6 dozen chocolate cookies and 7 dozen oatmeal cookies for $84. The bakery also sold another customer 1 dozen chocolate cookies for $7. How much do the cookies cost?
6 c + 7 o = 84
c = 7
so
6*7 + 7 o = 84
6 + o = 12
o = $6 per dozen and c = $7 per dozen