SOLUTION: Need help for this problem ty The volume of the frustum of a regular triangular pyramid is 135 cu. M . The lower base is an equilateral triangle with an edge of 9cm . The upper

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Question 969291: Need help for this problem ty
The volume of the frustum of a regular triangular pyramid is 135 cu. M . The lower base is an equilateral triangle with an edge of 9cm . The upper base is 8m above the lower base . What is the upper base edge in meters
Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
Did you really mean the mixed units of centimeters for the edge, meters for
the distance between bases and cubic meters for the volume?  If so be sure
to convert the centimeters to meters.

You need two formulas:

1. The volume of a frustrum of a pyramid:

V%22%22=%22%22expr%28h%2F3%29%28B%5B1%5D%2Bsqrt%28B%5B1%5DB%5B2%5D%29%2BB%5B2%5D%29

where h = height and B1, B2, are the areas 
of the two bases.

2. The area of an equilateral triangle:

A%22%22=%22%22expr%28sqrt%283%29%2F4%29%2As%5E2

where s is the length of each of the 3 equal sides of the equilateral triangle.

Step 1. Find the area of the lower base by substituting the given value for s
in the 2nd formula. The value you get for A will be the value of B1.   

Step 2. Substitute the given values for V, h, and and the value you got for B1 in 
step 1, into the first formula and solve for B2. This will involve
isolating the square root term, squaring both sides and solving a quadratic.

Step 3. Substitute what you got for B2 in step 2 for A in the second
formula, and solve for s.

Good luck.  Be sure you don't mix centimeters and meters. 

Edwin