b
\(\begin{array}{l}
{\rm{P = }}\mathop {\rm{F}}\limits^ \to \,.\mathop {\rm{v}}\limits^ \to \\
P\,\, = \,\,\left( {\,60\hat i\,\, + \;\,15\hat j\,\, - \,\,3\hat k\,} \right)\,.\,\,\left( {\,2\hat i\,\, - \,\,4\hat j\,\, + \;\,5\hat k\,} \right)\,\, = \,\,45watt
\end{array}\)