Calculating Speed

How long will it take for the girl to cycle 4 km? (The girl's speed = 8.5 m/s)

$\begin{array}{rcll} t &=& \frac{ 4\ \text{km} } { 8.5\ \frac{ \text{m} } { \text{s}}} \cdot \ \frac{ 1000\ \text{m} } { 1\ \text{km}} \\ &=& \frac{ 4\cdot 1000 } { 8.5 } \ \text{s} \\ &=& \frac{ 4000 } { 8.5 } \ \text{s} \\ &=& 470.588235294 \ \text{s} \\ &=& 470.588235294 \ \text{s} \cdot \ \frac{ 1\ \text{min.} } { 60\ \text{s}}\\ &=& 7.84313725490\ \text{min.}\\ &=& 7\ \text{min.} \quad 50.5882352940\ \text{s} \\ \end{array}$