Answer
a) $5.48\times10^6J$
b) $1310$ nutritional Calories.
Work Step by Step
a) The total amount of power Lance Armstrong generates is $\overline P=6.5\times75=487.5W$
We have $$\overline P = \frac{W}{t}=\frac{W}{\frac{s}{\Delta v}}=\frac{W\Delta v}{s}$$ $$W=\frac{\overline Ps}{\Delta v}$$
We know $\overline P=487.5W$, the length of the race $s=135km=1.35\times10^5m$ and his average speed $\Delta v=12m/s$, so $$W=5.48\times10^6J$$
b) The amount of nutritional Calories Lance Armstrong consumes is $(5.48\times10^6J)\times(2.389\times10^{-4})=1310$ nutritional Calories.
