Yes, you can find the same answer as separating the shaded area into a rectangle and a smaller triangle given by 4*6 + 1/2 * 4 * 4 = 24 + 8 = 32 m² if the dotted line is 6 m. But this answer is different from 36 m².

So the only conclusion is the dotted line cannot be 6 m. Logically if the dotted line is 6 m, one of the angle in the triangle must be 45º. But this is impossible if it is an right angle triangle, with sides 12 m and 10 m. So obviously, the answer of 36 m² is wrong.

I can’t solve this question using psle syllabus.

If in secondary school, you can use similar triangle to find the length of dotted line = 8 * 10/12 = 6.67 m

So the area of the shaded area = 4 * 6.67+ 1/2 * (10 – 6.67) * 4 = 33.34 m²

Or

12* 10/2 – 8 * 6.67* 1/2 = 33.32 m²