To get the value of x you need to use the Pythagorean Theorem
a²+b²=c² → 3²+b²=6.708204² (√45)
9 +b² =45.000001
-9 ↓ ↓-9
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zero pair √b² = √36.000001
b = 6
One side of the isosceles the x is 6, but we need the whole part so for last you just multiply 6×2= 12
The answer is...... X=12