21. For the demand equation, find the rate of change of price p with respect to quantity q. What is the rate of change for the indicated value of q? P=e^-0.005q ; q=100

Rick is driving to his uncles house in greenville,which is 120 miles from ricks town .after covering x miles rick she's a sign stating that greensville is 20 miles away. which equation when solved will give the value of x. a: x+120 = 20 b: x x120 =20 c: x +20 equals 120 d: x x20= 120