So we see one large triangle, that can be split into two triangles split by the thin dotted line:
- the First triangle --> has a hypotenuse of 26 and a leg of 11
- the Second triangle --> has a hypotenuse of 42
Let us find the other leg of the First triangle which also happens to be the height of the larger triangle, using the Pythagorean theorem

Thus the height of the entire triangle is 23.56 which also happens to be one of the legs of the Second triangle

Having found the other leg of the Second Triangle, we can find the base of the larger triangle is:
--> 34.77 + 11 = 45.77
The height as found in the first initial step is 23.56 thus the area is
Area =

Hope that helps!