How do I do these math word problems/?

Question

6: A boat went 15 km upstream in the same time it went downstream 45 km. The boat’s speed in still water is 10 km/h. What is the speed of the current?

5 km/h

6 km/h

7.5 km/h

9 km/h

7: Amanda can paint a room in ten hours. Michael can paint the same room in eleven hours. How long does it take for both Amanda and Michael to paint the room if they are working together?

Answer 1

Problem 7:

5 to 5.5 hours

If Amanda can paint a room in 10 hours, she can paint half the room in 5 hours.

If Michael can paint the room in 11 hours, he can paint half the room in 5.5 hours.

Answer 2

Boat question

v = d/t

velocity = distance/time

10kmph + speed of current (sc) = 45km / t

45 (10 + sc ) = t

10kmph - speed of current (sc) = 15km/t

15 (10 - sc) = t

therefore

45(10 + sc) = 15(10 - sc)

450 + 45sc = 150 - 15sc)

(450 + 45 sc) -150 = (150  - 15sc) - 150

300 + 45sc = 15sc

300 = -15sc - 45sc

300 = 60sc

therefore

sc (speed of current) = 5kmph

yup, complicated.

And for the 2nd question, I'd say 5 hours 15 mins (or 5.25 hours)

However if you want to be a little more accurate, to  3 decimal places it's between 5.238 - 5.239 hours (5 hours 14 mins 17 seconds - 5 hours 14 mins 20 seconds), but I doubt your teacher expects it that close.