4 A runner who is training for a long-distance race plans to run increasing distances each day for 21 days. She will run \(x \mathrm {~km}\) on day 1 , and on each subsequent day she will increase the distance by \(10 \%\) of the previous day's distance. On day 21 she will run 20 km .
- Find the distance she must run on day 1 in order to achieve this. Give your answer in km correct to 1 decimal place.
- Find the total distance she runs over the 21 days.