You throw a ball vertically upwards with an initial speed `v (in km per hour)`. The height `h` of the ball at each time `t`
is given by `h = v*t - 0.5*g*t*t` where `g` is Earth's gravity `(g ~ 9.81 m/s**2)`. A device is recording at every **tenth
of second** the height of the ball.
For example with `v = 15 km/h` the device gets something of the following form:
`(0, 0.0), (1, 0.367...), (2, 0.637...), (3, 0.808...), (4, 0.881..) ...`
where the first number is the time in tenth of second and the second number the height in meter.
# Task
Write a function `max_ball` with parameter `v (in km per hour)` that returns the `time in tenth of second`
of the maximum height recorded by the device.
# Examples:
`max_ball(15) should return 4`
`max_ball(25) should return 7`
# Notes
- Remember to convert the velocity from km/h to m/s or from m/s in km/h when necessary.
- The maximum height recorded by the device is not necessarily the maximum height reached by the ball.
def max_ball(v0):
    return round(10 * (v0 / 3.6) / 9.81)
def max_ball(v0):
    return round(10 * (v0 / 3.6) / 9.81)