Preston's Bakery sold one customer 4 dozen chocolate cookies and 9 dozen oatmeal cookies for $126. The bakery also sold another customer 8 dozen chocolate cookies and 5 dozen oatmeal cookies for $122. How much do the cookies cost?

Let's refer to the chocolate cookies using the variable c, and the oatmeal cookies using the variable o.

Using the information we have, we can set up two equations for the two different transactions.

4c + 9o = 126

8c + 5o = 122

Now, we need to solve for one of the variables in the first equation. I will solve for o.

4c + 9o = 126

9o = 126 - 4c

o = 14 - 4/9c

Next, we'll take this value for o and plug it into the second equation for the variable o. Then we can solve for c.

8c + 5(14 - 4/9c) = 122

8c + 70 - 2 2/9c = 122

5 7/9c + 70 = 122

5 7/9c = 52

c = 9

Finally, we can use the value of c and plug it back into the first equation to solve for o.

o = 14 - 4/9(9)

o = 14 - 4

o = 10

1 dozen chocolate cookies costs $9

1 dozen oatmeal cookies costs $10

Hope this helps!