Answer:
Option e) 320 s
Explanation:
Here, distance = 3.0 km = 3000 m
The velocity of boat when it is going upstream;
Upstream velocity = velocity of boat in still water - velocity of river flow
So, Upstream velocity 
So,Time to go upstream

The velocity of boat when it is going downstream;
Downstream velocity = velocity of boat in still water + velocity of river flow
So, Downstream velocity 
So,Time to go downstream

So, total time (t) = 
Option E is the correct answer.
1. Humidity cannot be used to predict rain.
2. I'm pretty sure it's weather but I'm not 100% sure. Maybe like 89% sure.
3. Tempurature doesn't affect humidity.
4. Not sure but I think its the 3rd one
Length of the pipe = 0.39 m
Third harmonic frequency = 1400 Hz
For the third harmonic:
Wavelength = 
The center of the open pipe will host a node and the nearest anti - node from the center will be at the 0.25 × wavelength
Distance from center = 0.25 × wavelength
Distance = 
Plugging the value of the length of the pipe (L) = 0.39 m = 39 cm
Distance = 
Distance from the center to the nearest anti - node = 6.5 cm
Hence, the nearest distance to the anti - node from the center = 6.5 cm
So, option C is correct.
First we have to find out the gravity on that planet. We use Newton second equation of motion. It is given as,
s = ut +(gt^2)/2
Distance s = 25m
Time t = 5 s
Velocity u = 0
By putting these values,
25 = 1/2.g.(5)²
g = 2
So the gravity on that planet is 2. Lets find out the weight of the astronaut.
Mass of the astronaut on earth m = 80 kg
Weight of astronaut on earth W = mg = (80)(9.8) = 784 N
Weight of astronaut on earth like planet = (80)(2) = 160 N
x = 160N