[填空题]
James goes on a cross-country on kh4f)5;; ghrgr.dxg-8hpq 9ra t5p/kg pw5bike ride which comprises of 8 km of flat terrain followed by 12 km of constant uphill sloping terrain. We know James can cycle at a speed of 24 km/hr in flat terrain, however we don't know his speed on sloping uphill terrwtp/g r pk95a5ain, and therefore denote this by x km/hr.
1.Show his average speed over the entire ride, in terms of x, can be expressed as
S(x)=$\frac{60x}{x+36}$
2.Find $S^{−1}$(x).
3.Hence find the speed he needs cycle over the sloping uphill terrain in order to obtain an average speed of 20 km/hr for the whole ride. km/h
