Question 1208106
The model is 
C=15.95+0.3940x+0.33606x for x<=50 this is C=15.95+0.73006x for x <=50; at x=50 charge is $52.45
C=52.45 (charge for 50)+(x-50)*0.10580+(x-50)*(0.3940)
C=52.45+(x-50)(0.4998) for x>50. So x=500 is 52.45+224.91=$277.36