I can't see pictures, but to find the area of a triangle, you multiply the dimensions, as you would a rectangle, but divide the area by 2.
For example, the dimensions of a triangle are 4 and 6.
Multiply the two.
4x6=24.
But don't stop there. Divide 24 by 2.
24/2=12.
So the area of the example triangle is 12.
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hope it helps