Area of a triangle is (base x height)/2

Since X and Y trisect QR, QX=XY=YR

In triangle PQX, QX is base
In triangle SRY, RY is base

Also, height of these two triangles is equal because they both are part of a same parallelogram

Since the base and height of the two triangles are equal, their areas are also equal

3 4 3