Your equation would be:
D. y = 10x + 6
Look up what is 75% of 31,500
100 - 20 = 80
179.00 = 80%
179.00 / 80 = 2.2375 = 1%
1% x 100 = 100%
So, 2.2375 x 100 = 100%
Therefore the original price was 223.75
10 goes into 67 six times making it 6 7/10, which cannot be simplified. Therefore, if can be left as it is, an improper fraction 67/10, or a mixed number 6 7/10.