Boat travels 210mi down and back, takes 10h down and 70h back, how do I set up the problem .. need current and still water speed

Can someone me and do the problem plz so i can understand it more better

Your friend uses c=50p to find the total cost, c, for the people, p, entering a local amusement park is the cost of admission proportional to the amount of people entering the amusement park? explain.

Which set of lengths could represent the sides of a triangle? a. 3, 7, 10 b. 4, 5, 10 c. 6, 8, 14 d. 12, 6, 7