For the triangle: Measure base x height divided by 2 = 4 x 3 / 2 = 12 / 2 = 6 km squared
Semi Circle: area of a circle = pi r squared = 3.14 x 2 km squared (half of the 4km diameter) = 3.14 x 4 (4 is 2 squared) = 12.56 divided by 2 (since it’s half of a circle) = 6.28 km squared