40 points please help me find each area of the triangle

9. 1/2 x 8 x 10 = 40 in²
10. 1/2 x 7 x 9 = 31.5 yd²
11. 1/2 x 12 x 8 = 48 cm²
12. 1/2 x 3 x 16 = 24 ft²