Answer:

Step-by-step explanation:
c varies jointly with d and the square of g


where, k is constant of proportionality.
Put the given value c = 30 when d = 15 and g = 2 and find out k


If c = 6 and g = 8 then d = ?



Hence, The value of d is 
The equation of the line is y=13x+133
100 / 32 = 3.125
3.125 * 18 = 56.25.
Stan's bike ride is 56.25 miles long.