The formula of a lateral area of a triangular prism is
LA = (1/2)*(perimeter of a triangle)*h
The perimeter of a triangle is the total of all sides.
Since the length of the base of a triangle is not given yet, use the Pythagorean theorem
base² = 7² + 24²
base² = 625
base = 25 cm
The perimeter is 7 + 24 + 25 = 56 cm
Finally the lateral area is
LA = (1/2)*56*30 = 840 cm²
