How do we find the Average Speed ?
The Average Speed is the distance traveled for the object, divided by the elapsed time taken to travel that distance, so the formula is :
S = D / T
where S = Average Speed, D = Distance, and T = Times
Here the object is the ball, the distance is 9 meters and the time elapsed for the ball to roll down the street is 3.5 seconds. Applying the formula we get :
S = 9 / 3.5 ≈ 2.6 metres per second
The ≈ symbols (which is the wavy equal sign) means we can't write the exact result, because there is an infinite quantity of numbers after the decimal point. So we need to give an approximation, since the result is 2.57142857142857...etc. we choosed to round up the result to 2.6.