Answer
$1220$
Work Step by Step
Formula to calculate the sum of an arithmetic sequence is: $S_n=\dfrac{n}{2}(a_1+a_n)$ ...(1)
Here, $a_1: $ First term and $d=$ common difference
Since, we have $d=a_2-a_1=10-4=6$
and $a_{20}=4+6(20-1)=118$
Then, our first (1) equation becomes: $S_n=\dfrac{20}{2}(4+118)=10(122)=1220$
