1. in equation = [p+a/v²] [v-b]=RT. what are the dimensions of a and b ? here p = pressure v = volume t =temperature.
2. write the dimensions of a and b in relations p = p-x²/at where p = power x= distance t= time.

This question requires you to understand that any physical quantity can only be added or subtracted from another physical quantity of the same dimension.

So, I can only add pressure to pressure, and not area or velocity or any other quantity. Similarly, volume may only be added or subtracted from volume.

So, in this question, p + a/v², what should be the unit of a/v² ? Think!

Yes, it would be same as that of p.

So, If p is in N/m² and v is in m³. 

a/v² = N/m²

or

a/m³ = N/m²

or

a = Nm.

Similarly, you can solve the other questions. Do get back to us if you have a doubt in any of the steps.