Math Word Problem
posted by Nicki .
Need a formula for this math problem. Help!?
Relinda owns a tea shop and is creating a new mix of tea for her customers. She is using a standard black tea that sells for $7 per pound and a special orange flavor that sells for $11 per pound. She is planning to make a 40 pound batch of the mix and would like to sel it for $8.50 per pound. How much of each tea should she mix if she is not planning on making or losing any money with this mix?
I'm thinking it might be 7x+11(40x) divided by 40 equals $8.50
My brain is melting!

The suggested formula is perfect!
Only thing to add:
x=number of pounds of black tea. 
jesse bought 6 onequarter pound bags of grape.how many pounds of grapes did jesse buy ?

5. At one gym, there is a $12 startup fee, and after that each month at the gym costs $20. At another gym, it costs $4 to startup, but after that, each month at the gym costs $22. After how many months will the cost of both gyms be the same?