availablity simply means when the unit is offered, sometimes a unit is offered many times in a year, for example, ACST101, it is offered in D1,D2,E1, so you have to choose a session to fit in your timetable.
I agree with u that it won't be better off, but i still jave different value of DWl.
the difference between the loss of total surplus and tax revenue is the DWL.
i think the loss in cosumer surplus is 0.5*14*(50/3-12)-0.5*17*(50/3-11)=-15.5
the loss in producer surplus is...
I'm afraid I have different thinking on the last part of question2. In this question, As the totol utility loss due to tax is 46 unit, but the total tax earns by government is 56. As the government will use the proceeds of the tax to finance public works, so I think the community is better off.