Okay, here we have this:
Considering the provided vertices, we are going to calculate the requested area, so we obtain the following:
Then we will first calculate the measure of each side and later with Heron's formula we will find the area, then we have:



Then, the area is:
![\begin{gathered} A=\sqrt{((√(13)+√(17)+√(20)))/(2)((√(13)+√(17)+√(20))/(2)√(13))((√(13)+√(17)+√(20))/(2)√(17))((√(13)+√(17)+√(20))/(2)√(20))} \\ =√(49) \\ =7 \end{gathered}]()
Finally we obtain that the triangle's area is equal to 7 square units.