The answer is 6 meters
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Step-by-step explanation:
The base length is 5 meters, so the square bottom face is 5*5 = 25 square meters in area
The lateral surface area is therefore 85 - 25 = 60 square meters, which is the total of the 4 triangular faces. Each of these faces are the same so each face is 60/4 = 15 square meters
Let L be the slant height
The base 5 times the slant height L over 2 will give us the area of each triangular face. In other words
A = 5*L/2
15 = 5*L/2
15*2 = 5*L
30 = 5L
5L = 30
L = 30/5
L = 6
So that's why the slant height is 6 meters