There are $3$ files to be stored on a tape so total permuation = $3! = \ 6$
$1) \ 3\rightarrow 5\rightarrow 10$ Access time = $3 \ + \ 8 + 18 \ \ = 29 $
$2) \ 3\rightarrow 10\rightarrow 5$ Access time = $3 \ + \ 13 + 18 = 34 $
$3) \ 5\rightarrow 3\rightarrow 10$ Access time = $5 \ + \ 8 + 18 = 31 $
$4) \ 5\rightarrow 10\rightarrow 3$ Access time = $5 \ + \ 15 + 18 = 38 $
$5) \ 10\rightarrow 3\rightarrow 5$ Access time = $10 \ + \ 13 + 18 = 41 $
$6) \ 10\rightarrow 5\rightarrow 3$ Access time = $10 \ + \ 15 + 18 = 43 $
Minimum$\{ 29,34,31,38,41,43\} = 29$