The approximate constant of variation?

Question

Kendra is pumping gas into her car, and the total cost for the gasoline, T, varies directly with the number of gallons, N, that she pumps. At 10.5 gallons pumped, Kendra's total bill is 29.40. What is the approximate constant of variation?

Answer 1

T=kN where T is the cost and N the number of gallons. 29.40=10.5k, so k=29.40/10.5=2.8