Salut/Hello!
Explanation:
You can use the explanation it has above (in the screenshot) to calculate.
The area of the rectangle or square is the length x width
For a square, all sides are equal so it's enough to just know one.
If you observe you can see how the area of the triangle is exactly half of the area of the square/rectangle. So if you struggle to find it using the formula 1/2 x base x height then you can simply divide the area of the rectangle with 2
Answer:
a. square 12 x 12 = 144 cm
triangle 1/2 x 144 = 72
and we know 1/2 is equal to 0.5
b. rectangle 11 ft x 5ft = 55 ft
triangle 1/2 x 55 = 27.5
... The rest aren't clear but with that example you can definitely do it on your own!
I hope it was useful! :]