q1> option d as at price ratio =1 , it would be competitive eqm..
q2> option a as only the 45 degree line will give all pareto efficient points.
q3> option c
q4> option b
( budget constraint for the one who is taxed => 0.5x +0.5y=50
budget constraint for the other person => 0.5x+0.5y=75
now work out in the same way)
:)