7. Sue is training for a marathon. Her training includes a run every Saturday starting with a run of 5 km on the first Saturday. Each Saturday she increases the length of her run from the previous Saturday by 2 km .
- Show that on the 4th Saturday of training she runs 11 km .
- Find an expression, in terms of \(n\), for the length of her training run on the \(n\)th Saturday.
- Show that the total distance she runs on Saturdays in \(n\) weeks of training is \(n ( n + 4 ) \mathrm { km }\).
On the \(n\)th Saturday Sue runs 43 km .
- Find the value of \(n\).
- Find the total distance, in km , Sue runs on Saturdays in \(n\) weeks of training.