Question 592710
let x be the side we are looking for, y the side that is 6 and z the hypotenuse

We know by the Pythagorean Theorem that ,  
 z^2  = x^2 + y^2     -->  x^2 =  z^2 - y^2  
                     -->  x =  sqrt( z^2 - y^2)   ( x can't be a negative number)
                    -->   x = sqrt( 10^2 - 6^2)  
                            = sqrt( 100-36)
                            = sqrt( 64)
                            =8

so the third side is 8 meters