Answer: (pr + 1)(q + 1)
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Work Shown:
Use the factor by grouping method to get the following.
pqr + pr + q + 1
(pqr + pr) + (q + 1)
pr(q + 1) + 1(q + 1)
(pr + 1)(q + 1)
We can use the FOIL rule, distribution, or the box method to expand out (pr+1)(q+1) to get the original expression again. This helps confirm the answer.