$$ \begin{cases} \Delta t &= 3.15\ut{h}\\ \Delta \vec r &= 11.2\i+24.5\j+2.88\k\ut{km} \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \bar v &= \frac{\Delta r}{\Delta t}\\ &= \frac{\sqrt{11.2^2+24.5^2+2.88^2}}{3.15}\ut{km/h}\\ &=\frac{2\sqrt{1834961}}{315}\ut{km/h}\\ &\approx 8.600681416985678\ut{km/h}\\ &\approx 8.60\ut{km/h}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} \vec n &= 0\i+0j+1\k,\..