Answer
$79.41\leq y \leq 93.05$
Work Step by Step
Based on the data, we have the regression line
$y' = 2.6623x + 64.936, n=9, \hat x=8, \hat y=86.23$
$c=0.95, \alpha/2=0.025, df=7, t_c=2.262$
$\sum (y-y')^2=56.67, s_e=\sqrt \frac{56.67}{9-2}=2.85$
$\bar x=7.41, \sum x=66.7, \sum x^2=536.0$
$E=2.262\times2.85\times\sqrt {1+\frac{1}{9}+\frac{9\times(8-7.41)^2}{9\times536-66.7^2}}=6.82$
Interval $(86.23-6.82, 86.23+6.82)$ which gives the y range $79.41\leq y \leq 93.05$
