Answer:
rectangle A's area: 12, 3 x 4 = 12
Area b: 1 x 4 = 4 divided by 2 = 2, the base is 1 height is 4. Multiply given lengths, then multiply by 1/2 because formula of a triangle is BH x 1/2. To get your answer of 2.
Area C: 3 + 5 = 8, 8 x 4 = 32, 32 divided by 2 = 16, formula of a trapezoid is base 1 + base 2 x height x 1/2. In this case 5 is your base and base 2 is 3. Add them up to get 8. We then multiply 8 by the height which is 4 if you count from the top to bottom in the middle. 8 x 4 = 32. 32 x 1/2 = 16 (basically just dividing by 2).