Explanation:
\({T=5}\) hours, \({r^{\prime}=4 r}\)
According to law of period, \({T^{2} \propto r^{3}}\)\({\left( {\frac{{{T^\prime }}}{T}} \right)^2} = {\left( {\frac{{{r^\prime }}}{r}} \right)^3}\) \({T^\prime } = {\left( {\frac{{{r^\prime }}}{r}} \right)^{3/2}}T = {(4)^{3/2}} \times 5 = 8 \times 5{\text{ hours }}\) \(\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 40{\text{ hours}}\).
So correct option is (3)