Answer
(a) $250\ sec$
(b) $0.3536$
Work Step by Step
(a) Given $t=31.293\ w^{-1.5}$, for $w=25\ lb$, we have $t=31.293\cdot 25^{-1.5}\approx250\ sec$
(b) $t_1=31.293\ w_1^{-1.5}$ and $t_2=31.293\ (2w_1)^{-1.5}$, thus $\frac{t_2}{t_1}=2^{-1.5}\approx0.3536$
