The value of a car is inversely proportional to its age. if a car is worth $49004900 when it is 55 years old, how old will it be when it is worth $35003500?
multiply them together to get a constant. Then divide the constant by the new value and it will give you the new age. You can just use substitution to find any variable.
constant = age * value value = constant / age age = constant / value
