$80 is the total.
You get a 20% discount.
We want the price after this.
20% in decimal (divide by 100) is:
20/100 = 0.2
So,
20% of 80 is:
0.2 * 80 = 16
Thus, you have $16 off of 80.
Your final total you would need to pay:
80 - 16 = $64
C is the correct answer.
