normal distribution, mean = 80 and standard deviation = 5. score? separates the top 10% of the scores from the lowest 90% of the scores

Question

Checking my work: M = 80 SD = 5 X = ? scored 90% better than others. Closest area from table was .8997 giving a z-score of 1.28.

using the formula z = (x - M)/SD, my answer is 86.4