This is similar to the question before. Remember that the height of a triangle is drawn 90 degrees from the base (see the little square), meaning that the height is 6.9 cm. And the base is the line the triangle is standing on ( which is 8.4 cm)
Then put them into your formula base x height / 2
6.9 x 8.4 / 2 = 28.98 cm squared