3.03 days
Step-by-step explanation:
We first look up the Z-score for 90th percentile in the table;
= 1.282
Z score is given by the formula;
X – μ / σ
We are given μ as 5.2 while σ is 2.2. Therefore;
1.282 = X - 5.2 / 2.2
1.282 * 2.2 / 5.2 = X
3.03018 = X
= 3.03