Let us take a projection of the square PORS about the edge QR as shown below:
Using projection of the figure through a mirror image we can see that: TU + US = TU + US’ Minimum value of (TU + US') will be when the points T, U and S’ lie on a straight line. In that case TU + US' = TS' =√(3)2+(2)2=√9+4=√13