有关初中代数分数和公式的数学题

有关初中代数分数和公式的数学题
I am a S2 student ,the following Maths question that I would like to ask for help.Thanks
1.In the process of designing the structure of a stadium,the relation among the time for the crowd (t minutes),the number of people in the stadium(N),the number of passages(n) and the width of each passafe (w m)are considered,and the following formula is obtained:
t=3+ N / 8 nw
(a) It is known that at the end of a match,there are 7 200 people leaving the stadium.If 10 passages of 6m wide each are opened up for people to pass through,how long will it take to clear all the people?
(b) Make n be the suject of the formula.