step 1
Find out the price of one CD
Divide $15 by 5
15/5=$3 each CD
step 2
Find out the price of one vinyl record
Divide $40 by 4
40/4=$10 for each vinyl record
step 3
Let
x -----> number of CDs
y ----> number of vinyl record
the linear equation that represents this problem is
3x+10y=120