我想問一條F.6 Physics關於relative velocity既問題（高考題目）請求幫忙＞＜

A man swims across a river 100m wide always leaning upstream at an angle of 30 with the bank.

1.How long does he take to across the river if he swims at 4m/s and the water flows at 16m/s?
2.How far upstream from the point at which he would be reached if the water is still,assuming that he keeps swimming straight.

其實我想知ｌｅｅ個ｔｏｐｉｃ大概會點問，有冇特定方法做，係咪顯顯差唔多，識做ｌｅｅ題係咪等於識計其他？（我備緊課，望有高人指點＞＿＿＜）

Ｔｈａｎｋｓ　ｘ　９９９９９９９９．．．．