We'll recall the following formula that gives the area of a triangle:
A = side*side*sine of the angle included/2
Since the lengths of the sides of an equilateral triangle are equal, let the length of the side be x.
A = `x^(2)` * sin 60/2
10.2 = `x^(2)` *`sqrt(3)` /4
40.8 = `sqrt(3)` `x^(2)`
x = `sqrt(40.8/sqrt(3))` m
x = 4.853 m
Therefore, the requested length of the side of equilateral triangle is x = 4.853 m.