Your in luck! I was just learning these percent things today 'xD but Not in luck at the same time. I will answer the 2 questions that's the most I can do.
1. $17.50 with a 7% sales tax
Answer: 17.50 times .07 equals 1.23
17.50 plus 1.23 equals 18.73
The answer is $18.73
2. 21.95 with a 4.25% sales tax
Answer: 21.95+4.25=26.20
Hope this helps!! :D this took me a while to figure out and used a bit of my time. So I hope the time was worth it! :)