Answer
$s_{b_1}=0.2055$
Work Step by Step
$s_e=271.042$ (item (b))
To find $s_x$:
Using the EXCEL, enter the "7-day strength" values in the column A.
In A11 enter "=STDEV.S(A1:A10)"
$s_x=439.591$
$s_{b_1}=\frac{s_e}{\sqrt {∑(x_i-x ̅)^2}}=\frac{s_e}{\sqrt {n-1}s_x}$ (see note on page 684)
$s_{b_1}=\frac{271.042}{\sqrt {10-1}\times439.591}=0.2055$
