Find the multiplier that links the known terms, then apply it to all unknown terms.<br><br>
&bull; The middle term changes from 6 to 42: 42 ÷ 6 = 7 (multiply by 7).<br>
&bull; First term: 1 × 7 = 7<br>
&bull; Third term: 3 × 7 = 21<br>
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Final Answer: A = 7, B = 21