Persons A and B are moving at constant speeds of 5 ms \( ^{-1} \) and 4 ms \( ^{-1} \) , respectively as shown in the figure. Find out the relative velocity of B with respect to A.

A 16.12 ms \( ^{-1} \)

B 6.26 ms \( ^{-1} \)

C 12 ms \( ^{-1} \)