You can put this solution on YOUR website! the x dimension is the difference in the first two points (where y is constant)
__ -0.1-(-7.9)=7.8
the y dimension is the difference in the 1st and 3rd points (where x is constant)
__ 6.8-(-3.4)=10.2
the area is just x times y __ 7.8*10.2
this works because the rectangle is oriented in line with the axes
__ if it were tilted, you would have to use the distance formula to find the lengths of the sides