Explanation: A triangle's area is defined by the formula; height × 1/2 base. BUT it has always been easier for me to do height × base then divide by 2.
3 × 6 = 18 18 ÷ 2 = 9
or if you prefer traditional; 3 ÷ 2 = 1.5 1.5 × 6 = 9
Both equal 9.
Now you move onto the rectangle. Formula: height × length 16 × 8 = 128