Hello, some of your questions are slightly blur due to the picture quality. Nonetheless, here are the answers in clockwise direction (starting from top left). I hope that I have read Q3 and Q4 correctly.
Q1. Your answer is correct.
Q2. Area of triangle B is 120cm^2.
Formula for Area of triangle = 1/2 x base x height
= 1/2 x 12 x 20
Q3. 2 units = 156 stamps
3 units = 234 stamps
Q4. Area of shaded part = 1/2 x 14 x 10 =70cm^2
7 units -> 70cm^2
2 units -> 20cm^2 [unshaded area]
Total area of the whole figure= 70 + 20 + 20 = 110cm^2.
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