A sequence is defined by a_n = 3n - 2. What is a_10?

Substitute $n=10$ into the rule: $a_{10}=3(10)-2=30-2=28$, choice J. Choice H ($30$) drops the $-2$ and gives only $3n$. Choice G ($32$) adds $2$ instead of subtracting it, since $30+2=32$. Choice F ($18$) corresponds to $n=\frac{20}{3}$, not a term number, so it does not follow from the formula for any valid $n$. As a check, the sequence $1, 4, 7, 10,\dots$ increases by $3$ each term, so by the tenth term it has grown by $9\cdot3=27$ from the first term, giving $1+27=28$, which agrees with the substitution.