You can see from the bar graph that the unit is meters per second, so the number listed on each material is equal to the distance in meters travelled in one second.
For 21., we see that sound travels 346 meters in 1 second, so we need to multiply that by 20.
346*20=6920
21. 6,920 m
We will use this to answer number 22. We see that stone travels 5,971 m/sec, so we multiply that by 12.
5971*12=71652
22. 71,652 m
For 23 it says estimate, but I will use the actual amounts instead.
Stone: 5,971*17=101,507
Aluminum: 5,000*17=85,000
To find the amount: 101,507-85,000=16507
23. 16,507, or if you want the “estimated” answer, 17000