the OA is B. Please explain!

(1) alone:
obviously INSUFFICIENT, because we have no rule dictating how the table works.

(2) alone:
given all the Q's in the table, use this rule to fill in the other squares of the table in terms of Q. you can fill in the table from left to right and/or from top to bottom, following the rule repeatedly.

Q ..... Q ..... Q ..... Q

Q ... 2Q ... 3Q ... 4Q

Q ... 3Q ... 6Q ... 10Q

Q ... 4Q ... 10Q ... 20Q

as you can see, the bottom right square must contain 20Q, so it follows that Z must equal 20Q.
we don't have a numerical value for Z or Q unless we take both statements together, but note that this is immaterial: all that matters is the relationship between Z and Q, which is completely determined by (2) alone.

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