Explanation:
the area of a triangle is always :
baseline × height / 2
the height is the line from the vertex opposite of the line we choose to be baseline to the baseline in a right (90°) angle.
and yes, that applies also to heights that actually land outside the triangle, like in this example.
so, the baseline here is 11, the height is 7.
the area is :
11 × 7 / 2 = 77/2 = 38.50