Explanation:
average speed = total distance travelled / total time travelled
time to travel the first 6km: 6 / 50 = 3/25 (h)
time to travel the next 6km: 6 / 90 = 1/15 (h)
[I think there's problem in the question 'cause 900km/h sounds impossible for normal person to travel in normal condition]
The total time: 3/25 + 1/15 = 14/75 (h)
Average speed over the 12 km drive will be:

You put your 5 fingers up then you put 4 fingers up on the same hand
Levers
Most machines in your body are levers that consist of bones and muscles. Tendons and muscles pull on bones, making them act as levers. Joint, near where tendon is attached to bone acts as fulcrum. Muscles produce input force.
Answer:
True
Explanation:
Signals used for transmitting information contain many frequencies. Signal Bandwidth refers to the difference between the highest and lowest frequencies of the continuous band. In other words, a signal bandwidth is a range of frequencies.
B.W. = f₂ - f₁
It is measured in Hertz (Hz or per second).
Thus, the given statement is true.