For problem #1:  y  =  5x
  
 To figure out what happens when x doubles, choose a beginning value for x (perhaps choose 10) and put this number into
 the formula:  y  =  5(10)  =  50   --->   So when we start with 10 for x, we end with 50 for y.
  
 Now, to figure out what happens to y when we double x, let's double our value for x (now it's 20) and put this
 number into the formula:  y  =  5(20)  =  100  --->  So when x is 20, we end with 100 for y.
  
 Now, let's compare our final value of y (100) with our first value of y (50).
 Is 100, 50 multiplied by 2?
 Or, is 100, 50 multiplied by 5?
 Or, is 100, 50 divided by 2?
 Or, is 100, 50 divided by 5?