A quick way to crack these which-tile-generates-the-figure questions is to first sort the four candidates by how they differ from each other, since these questions typically change just one or two cells or mirror one arm between the near-identical options, then check only those changed spots against the given figure.
P: Compared with the other three tiles, P has an extra black cell tucked into what should be a white gap near one corner. Checking that exact corner in the given strip shows a white gap there instead, so P is ruled out.
Q: Every distinguishing cell in Q, the corner notches, the bends in the black steps, and the isolated white cell in the middle, matches the corresponding spot in each repeated block of the strip. No mismatch turns up anywhere Q is checked.
R: R has one step running in the mirrored direction compared with Q, near the lower edge. The given strip does not show this mirrored step, so R is ruled out.
S: S is missing a black cell that both Q and the given strip clearly show along one edge. That missing cell rules S out.
Since only Q agrees with the strip at every one of these distinguishing spots, Q must be the tile the strip was generated from.
Let's summarize:
Instead of comparing entire tiles cell by cell from scratch, find the few cells where P, Q, R, and S actually differ from each other.
Check only those few cells against the given figure, which is far faster than a full scan.
Whichever candidate agrees at every distinguishing cell is the generating pattern, here that is Q.
