The answer if 5.7 was the B and 4 cm is H then it’s 11.4. If 4 cm was the height and 13 was the base, it would be 26. If 5.7 was the base and 13 was the height, it would be 37.05 ( It goes the other way around to for the height and base). How to ever find the area of a triangle: b x h / 2 = x (x=area).