The average speed is the ratio between the distance covered, and the time elapsed to cover that distance.
The total distance is the sum of the three distances covered:

Similarly, the total time elapsed is

So, althought you didn't always travelled with the same speed, you globally covered 170km in 1.75 hours. This leads to an average speed of

Answer: -640, 2560
each number in the sequence is multiplied by -4 to get the next answer
9 - 6 = 3
so 3 + 6 = 9 which is an addition equation that helps you find the answer.
1.44 per kg
take 1.3 x 2, then subtract 12.7, finally divide that by 7