If you can recognize that this triangle is a right-triangle, it would be simple to find the height=6, and base = 1 from the coordinates, and the area would be A=(bh/2)=6*1/2=3 square units.
It can be recognized as a right-triangle because two pairs of coordinates share common values, A(-1,0), C(0,0), so the base is 1-0=1 unit. Similarly, from B(0,6), C(0,0), we see that the height of the triangle is 6-0=6 units.
If it is not obvious, we only have to plot the three points on square paper, on a graphing software, or on your favourite calculator. The image is shown attached.