9 oz of Ted's special coffee blend was made by combining 3 oz of brand X coffee which costs $6/oz with 6 oz of brand Y coffee which costs $12/oz. What is the cost per oz of the mixture?
Start by describing what we know
cost of brand X = 6 $/oz
cost of brand Y = 12 $/oz
9oz Ted's = 3oz brand X + 6oz brand Y
so 9oz Ted's costs
write this as a formula, (let cost/oz of mixture = T)