What if its "greater than 9"

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

Ab and bc form a right angle at point b. if a= (-3,-1) and b= (4,4) what is the equation of bc?

Which of these numbers of simulations of an event would be most likely to produce results that are closest to those predicted by probability theory? 15, 20, 5, 10