Question 862956
Total points available are 10 * 20 = 200
Note that you only have 8 scores noted.  Let's call the 9th a 16 (change the equation value if it's more/less)
Total points already scored = 14+18+16+16+18+15+20+19+16= 152
Points you want to have = .85 * 200 = 170
Points you need to get on next test = 18 (170-152)