Answer
$1.32$
Work Step by Step
Note that $\sec {x}=\frac{1}{\cos{(x)}}$. Hence, $\sec^{-1}{x}=\cos^{-1} {\left(\frac{1}{x}\right)}$.
Use a calculator in radian mode, use its inverse cosine function and round the result to two decimal places to obtain:
$\sec^{-1}{(4)}=\cos^{-1} {\left(\frac{1}{4}\right)}\approx1.32$