1). the submarine is descending 100 feet per minute. this is because the line decreases 100 on the y axis when the x axis increases by 1.
2). the submarine is descending 50 feet per minute. this is because the line decreases 50 on the y axis when the x axis increases by 1.
3). y=15x this is because the slope increases by 15 on the y axis when 1 is increased on the x axis. the y intercept is 0. this means that every hour of piano lessons they get paid $15.
I hope this helps, and hopefully I’m right :)