I need help writing a system of equations to model each of the following situations. You do not need to solve the systems.

Question

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) Sean 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 portion of each alloy to produce 500 g of a new alloy that is 75% copper.

Answer 1

C=.99S

C= .89S + 12

The 2nd cost is less if .89S+12 < .99S

(.99-.89)S > 12

.10S > 12

S>120 songs

15S+25D = 475

S+D =25

15S + 15D = 375

10D =100

D=10

S = 15

65x + 90(500-x) = 75(500)

65x-90x = (75-90)500

35x = 15(500 = 7500

x = 7500/35 = 2500/7 = close to 357 of 65% copper

500-x = close to 143 of 90% copper

to get 500 of 75%