we want to identify with transformation was applied to the triangle to get the one on the left. Note that a translation would leave the triangle in the same orientation. As the triangle on the left does not have the same orientation as the one on the right, we can immediately discard option C.
Also, note that when we reflect on the x axis, the x coordinates are still the same. This means that under a reflection on the x axis, the triangle should remain on the same "side" of the plane. That is, on the right. As the triangle on the left is on a the left side of the plane, we can also discard option A.
So the only remaining options are B and D.
Recall that a rotation about a points means that we are keeping that point fixed.
Also, remember that if we are rotating counterclockwise, we are rotating on the opposite direction as the clocks normally rotate.
Note that if we apply a 90° rotation counterclockwise about the origin, we would get the following triangle
which doesn't look like the triangle we are given. So we can discard option B as well.
This means that the correct option is option D