Question 1017191
Shoelace theorem


1.....1
6.....2
8.....5
1.....1


left to right: 1*2 + 6*5 + 8*1 = 40
right to left: 1*6 + 2*8 + 5*1 = 27


area = 1/2 * |40 - 27| = 6.5