A boat is able to move through still water at 20 m/s. It makes a round trip to a town 3.0 km upstream. If the river flows at 5m/s ,the time required for this round trip is:
a) 120s
b) 150s
c) 200s
d) 300s
e) 320s

Time required for round trip is 320 s.

Explanation:

Given :

Velocity of boat in still water , v = 20 m/s.

Velocity of river , V = 5 m/s.

In the given question boat make round trip to a town 3 km upstream.

Therefore, Total time = time taken in upstream + time taken in upstream.

We know ,   ( here all have their usual meaning ).

Total time ,    ( upstream velocity = 20-5 = 15 m/s.

                                                              downstream velocity = 20+5 = 25 m/s)

Hence, this is the required solution.

i think its

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.