Don, an office equipment sales representative, earns a weekly salary plus a commission on his sales. One week his total compensation on sales of $5000 was $660. The next week his total compensation on sales of $8000 was $810. Find Don's weekly salary and his commission rate.
with a % of p, we have
check = salary + pct * sales
c = s + px
s + 5000p = 660
s + 8000p = 810
subtract and you get
3000p = 150
Now finish it off