I would use the method of 'backward fell swoop' in which validity follows, if by taking the conclusion to be false, it renders the premises false.*
In this case, choosing S false clearly gives either Q or R ( or both) false in 3. and P or R false in 2, thereby making 1 false since at least one of Q, P or R must be false. Therefore the argument is valid.
*Refer to the truth table for >
to understand this. The premises are a conjunction >