\frac{1}{125} s \Rightarrow u = 2, 25 \frac{m}{s} \Rightarrow v = 4 u = 9 \frac{m}{s}

${\frac{1}{125}\,\mathrm{s} \Rightarrow u = 2,25\,\mathrm{\frac{m}{s}} \Rightarrow v = 4u = 9\,\mathrm{\frac{m}{s}}}$

Error