20
21
22
23
Correct answer is D
Tn=a+(n−1)d (for a linear or arithmetic progression)
Given: Tn=71,a=−6,d=−212−(−6)=312
⟹71=−6+(n−1)×312
71=−6+312n−312=−912+312n
71+912=312n⟹n=8012312
=23
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