What are the challenge encountered during the given activities​

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

What is the slope of the line shown below?

Avery’s piggy bank has 300 nickels, 450 pennies, and 150 dimes. she randomly picks three coins. each time she picks a coin, she makes a note of it and puts it back into the piggy bank before picking the next coin.