Managerial accounting/algebra help?

So this problem is confusing me a little. It's related to Job-Order Costing and says:

"Job 218 was one of the many jobs started and completed during the year. The job required $3,600 in direct materials and 400 hours of direct labor time at a rate of $11 per hour. If the job contained 500 units and the company billed at 75% above the unit product cost on the job cost sheet, what price per unit would have been charged to the customer?"

So I know that unit product cost = total product cost (which is direct materials+direct labor+factory overhead) / number of units

But I don't have the factory overhead amount so how do I solve for the unit product cost?! I'll admit I haven't done algebra in a while... I tried the whole isolating the one variable in order to find the other and coming to the answer that way but then that failed, but I don't know if it's because I wrote the equation wrong. When I tried that, I used:

.75y+y=(3,600+4,400+x)/500

And got y=1 but that doesn't make any sense because that should be the unit product cost.

What am I doing wrong? What am I not seeing?

Thanks in advance for the help!