Using Summation Notation

According to the notation, the lower limit of summation is 3 and the upper limit is 7. So we need to find the sum of $k^2$ from $k=3$ to $k=7.$ We find the terms of the series by substituting $k=3\text{,}4\text{,}5\text{,}6\text{,}$ and $7$ into the function $k^2.$ We add the terms to find the sum.