Look at the units column. Which units exist that, when multiplied by themselves, give a number ending in the same digit?
. This works, but evidently isn't a possibility as multiplying anything by will give .
This works, but again isn't a posibility for Q due to it being too small.
This doesn't work.
Again, this doesn't fit.
Keep going along this route. The possibilities for Q vanish quickly, and then consider the possibilities for P given the options for Q.