Answer: -
0.2 Kg
Explanation: -
The equation used by Rhia for the carbon footprint measurement is
C = 0.2 B + 0.1 S
where S miles are by subway, B miles by bus and C is Kg of carbon dioxide.
From the equation we see the coefficient of B is 0.2.
Thus 0.2 Kg of carbon dioxide per mile the bus portion contributes to Rhia's carbon footprint.