As per the problem we have
Mark wants to measure the length of the lake from point C .
Mark measured 11 feet to one side of the lake and 15 ft to the other side of the lake.
Since the distance to one Side from the point C is 11 feet and 15 ft to the other side.
Hence the total distance will be just the some of the two distances and it is
![=11ft+15ft=26ft\\\\\text{Hence length is }26ft\\](https://img.qammunity.org/2019/formulas/mathematics/middle-school/946j8df5swyfubxmjqo6jzqw4zntjien5v.png)