How many terms (summands) are in the sum? I realize there are similar stacks to my question such as:
How many summands are there
Although I require further clarifications to understand.

Consider the sequence: 4 + 11 + 18 + 25 + ... + 249.

1) How many summands are in the sum.
2) Compute the sum.

Since there are $36$ terms as observed by the other answers the sum of the arithmetic progression is
$$
\frac{\text{number of terms}\left(\text{first}+\text{last}\right)}{2}=\frac{36(4+249)}{2}=18(253)=4554.
$$
