René Descartes ( March 31, 1596 – February 11, 1650), also known as Cartesius, was a noted French philosopher, mathematician, and scientist. Dubbed the "Founder of Modern Philosophy" and the " Father of Modern Mathematics," he ranks as one of the most important and influential thinkers of modern times.
So attached is the plotting of the triangle and I estimated it's area to be 7 squared units (OPTION C).
Note: in the graph i used colour codes to represent those partial squares that I used to counted as one and the gray squares are the naturally whole ones.