Actually Welcome to the concept of Areas,
Let's divide the above map in to 2 parts , that is a rectangle and a triangle, and add both thier areas to get the area of the Nevada.
so we get as,
Area of triangle = 1/2*b*h
Area of triangle ==> 1/2*309*306 ==> 47277 mi^2
Area of rectangle = l*b = 205*309 ==> 63345 mi^2
Area of NEVADA = 47277 + 63345 = 110622 mi^2
hence the area = 110622 mi^2