The constant of proportionality should be 45 miles per hour, and the car should travel 135 miles in three hours.
First you cross multiply.
2*(b-4)=6b
Then distribute the 2.
2b-8=6b
Minus 2b from each side.
-8=4b
Divide each side by 4.
-2=b
So -2 is your answer.
It should be C english :)