Question 1124614
On the one hand there is a cost equation.  This represents the money he needs to spend (in dollars) to make x cookies:
C(x) = 120 + (0.1)x  <br>

Now when he sells cookies, there is a revenue equation for x cookies sold.  This represents the money he takes in:
R(x) = (0.5)x <br>

He breaks even when R(x) = C(x):
(0.5)x = 120+(0.1)x 
(0.4)x = 120
        x = 120/(0.4) = 300<br> 

You can also plot R(x) and C(x) to see where they intersect.