Answer:
save $3.6, pay $14.4
Explanation:
A cd costs $18
If there is a 20% discount, you only have to pay 80% of the original price.
This means you only have to pay (0.80 x $18=) $14.4 dollars, which means you saved ($18 - $14.4=) $3.6.
Or you could just do $18 x 0.20 = $3.6