Answer:
a = mh
where m is the rate of income of Maria by babysitting per hour.
Explanation:
Let the amount that Maria makes is $a for babysitting for h hours. 
If the rate of income i.e. slope of the graph obtained from plotting the number of hours along the x-axis and her earning in dollars along the y-axis will be given by 
 {Since Maria will make $0 for babysitting for 0 hours}
 {Since Maria will make $0 for babysitting for 0 hours} 
⇒ a = mh 
where m is the rate of income of Maria by babysitting per hour. (Answer)