Two people, A and B, ride bicycles from the same place at the same time, and A travels 15.8 kilometers per hour, how much. How many hours have passed since the distance between the two is 20 kilometers? Fill in the appropriate conditions to make it a two-step calculation problem, and then answer it.
甲、乙两人骑自行车同时从同一地点相背而行，甲每小时行驶15.8千米，多少．经过多少小时两人相距20千米？填上合适的条件，使其成为一道两步计算的应用题，再解答．
<result>9.2</result>