Help me Please!! I need help with math again

How do you find the area of a triangle

The clayton family’s pool has vertices at the coordinates (0, 2), (0, 5), (2, 5), (2, 6), (5, 6), (5, 1), (2, 1), and (2, 2). if each grid square has an area of 9 square feet, what is the area of the pool?

Find an bif a = {3, 6, 9, 12) and b = {2, 4, 6, 8, 10).