Question

A special box designed to hold an antique artifact is shaped like a triangular prism. The surface area of the box is 421.2 square inches. The height of the base triangle is 7.8 inches and each side of the base triangle is 9 inches long. What is the height of the box?

Answer 1

The area of the base is:
A = root ((s-a) * (s-b) * (s-c) * (s))
Where,
a, b, c: sides of the triangle
s = (a + b + c) / 2
We have then:
s = (9 + 9 + 9) / 2
s = 13.5
A = root ((13.5-9) * (13.5-9) * (13.5-9) * (13.5))
A = 35.07
Then, the surface area of the prism is:
S.A = 2 * A + 9h + 9h + 9h
Where,
h: height of the prism:
Substituting values:
421.2 = 2 * (35.07) + 9h + 9h + 9h
Clearing h:
27h = (421.2 - 2 * (35.07))
h = (421.2 - 2 * (35.07)) / (27)
h = 13
Answer:
the height of the box is:
h = 13 inches