Given the first term is 3 and the last term is 39.
Recall that the sum is given as:
[tex]S_n=\frac{n}{2}(a_1+a_n)[/tex]Substituting in the above equation gives:
[tex]\begin{gathered} S_n=\frac{10}{2}(3+39) \\ S_n=5(42) \\ S_n=210 \end{gathered}[/tex]Therefore, option (a) is correct.
