is the B different than b or are those the same variable. if they are then you would expand the equation to b^2 + b -6 = -6 then solve for b which would give you 0 and 1. if they are not the same then you would need to move things around and get -6/(B+2) + 3= b.
the best method to calculate this is to take 1lawn per 3hours and add 1lawn per 3 hours and determine the amount of lawns they could both do. then reduce to one lawn. this should give you 1.875 hours or 1 7/8 hours.
I am assuming that you are in a calc based physics. You should know that the derivative of position is velocity and the derivative of velocity is acceleration. first derivative is (2t,-3t^2) the second derivative is (2,-6t) when you plug in 1 you get (2,-6).
In order to answer this you take 1 divided by 8 then multiply by 100. the answer should be less than 100 if you did it properly.