The pressure of a gas changes linearly with volume from A to B as shown in figure. If no heat is supplied to or extracted from the gas then change in the internal energy of the gas will be

 

work = area under P-V curve $=-4.5\mathrm{J}$

According to first law of thermodynamics :

$\mathrm{Q} = ∆\mathrm{U}+\mathrm{W}$

Since, its given in question that Q is zero, 

$\Rightarrow ∆\mathrm{U} = -\mathrm{W}$

Therefore change in internal energy = -(-4.5J) = 4.5J