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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

The graph of g(x) = -x^2 is a reflection in the x-axis of the graph of f(x) = x^2. Both graphs have one x-intercept as both graphs have their vertices at the origin, (0,0).
Eighty nine crore, six lakh, seventy eight thousand and three hundred forty.