1. Release of gases
2. Bubbling
3. And change in color- this one can also be for a physical change.
Hope this helps.
Average speed is defined as total distance moved in total interval of time
so it is given as

now here is we show distance by "d" and time by"t"
then we will have mathematical expression as follows

Here try this. The pic is the answer
Answer is 76,352 just look it up