Answer
n=26
Work Step by Step
The n th term can be calculated as:
$a_n=a_1+d\times(n-1)$
Here: $a_n=210$ and we have to find $n$.
In an arithmetic sequence, first we have to find the common difference, which can be calculated as the difference of any two subsequent terms:
$d=a_2-a_1=18-10=8$.
By substituting we get:
$210=10+8\times(n-1)$
$n-1=\frac{210-10}{8}=25$
$n=26$
