How to fill an area bounded by some lines?

In "Corel Draw X6" there are drawn lines which overlap ever so slightly to make it appear as a closed figure. How can I fill the area that is bounded by mentioned lines (because now it is transparent)?

Sorry for a probably silly question. I'm actually a mathematics student, not a graphics person, but I need to make some changes from time to time and university offers only fancy tools such as "Corel Draw".