Where are the questions so that I can deliver a more accurate answer.
Decreased it because you can float a lot
A- by kicking the ball into the net/goal
To begin with, we can use the formula that links frequency, wavelength and velocity.
Because you already have the wavelength and the frequency, you just need to solve for velocity. You can do this by multiplying each side of the equation by frequency.
Therefore, 400 x 2.5 = 1000m/s.
Hope this helps :)