Answer:
part one:
6 3
22 1
30 0
part two:
0.50*s+4*a=15
Explanation:
part one:
firstly:
6 individual songs cost 6*0.50= 3 dollars
she has 15 dollars so after downloading 6 individual songs that cost 3 dollars together
it means that she has only 15-3=12 dollars to download full albums
so 12/4=3 albums
because 4 dollar cost one album and with 12 dollars she can buy just 3 albums
secondary:
she downloaded 1 album
and one album cost 1*4=4 dollars
she has 15 dollars ,after buying 1 album
she has 15-4=11 dollars
so she can download 11/0.50=22 individual songs
so she can download 22 individual songs.
the last one:
she downloaded 30 individual songs
that all together cost 30*0.50=15 dollars
but she has 15 dollars at all so she cant buy any album because she spent all her money in individual songs.
because 15-15=0 money left
part two:equation
0.50*s+4*a=15