Charlie sells cookies only in packages of 10. it costs him $3.50 in materials per package. additionally, he has overhead costs of $1,500.00 per month. in order to pay himself a monthly salary of $5,000.00, how many packages of cookies does charlie need to sell per month at $10.00 per package?

Let x represent the number of packages Charlie needs to sell to make a monthly income of $5, 000 
Since he sells cookies only in packages of 10 then he has to sell 10x to make that income. But Charlie has expenses that has to be deducted from his total sales to make that figure.  
So the total expenses is $1, 500 in overhead and an extra $3.50 per material per package. So the total expenses = 1500 + 3.50x 
If he has to make $5, 000 at the end of the month we have
 10x - (1500 + 3.50x) = 5000
 10x - 1500 - 3.50x = 5000
 6.50x = 5000 + 1500 = 6500
 Solving we find:
 x = 1, 000 packages