Write a system of equations to model each of the following situations. You do not need to solve the systems. a. One website charges $0.99 per song download. Another website charges a one-time user fee of $12, but only charges $0.89 per song download.
b. Sea operates a lawn-cutting business. He charges $15 for a single lawn and $25 for a front and back lawn. Sean made $475 from 25 customers.
c. Brass is an alloy made by melting and mixing copper and zinc. A metallurgist has two brass alloys, one that is 65% copper and one that is 90% copper. He would like to combine a porion of each alloy to produce 500 g of a new alloy that is 75% copper.