Internal energy and expanding gas

[tomahawk1985]

17x10^5 joules are absorbed by an expanding gas that does 8x10^5 joules of work. (a) Find ΔU; (b) Assuming it expands at constant pressure, what's the change in volume?

Am I correct to use this:

ΔU = Q - W

Then after finding ΔU,

PΔV = Q - ΔU

Or does this make no sense?

 

[voko]

Both equations are OK. Except the second one is not really required, since you are given W directly.