Lets call s the number of scented candles sold, and u the number of unscented candles sold and write as an equation the info provided in the problem: 16s + 10u = 400 s + u = 28 that is, the first equation synthesize the fact that the amount of unscented candles times its quantity plus the amount of scented candles times its quantity equals $400 and the second equation synthesize the fact that the number of scented and unscented candles add up to 28 Now you just need to solve the system of two linear equations with two unknowns to get the specific value of the scented and unscented candles.
You don't have to use a formula, all you have to do is use basic algebra to modify the equation in front of you. Simply divide both sides by 2pi and you will end up with C/2pi = r. Then, just type it into your calculator and you're good to go!
