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3√2 units

Step-by-step explanation:

We can see that the line the triangles share bisects the right angle.  This means that each smaller angle is 45°.  

This makes each smaller triangle a 45-45-90 triangle.  This means the relationship between the sides is t, t, t√2; this means that the two legs of the triangle are equivalent and the hypotenuse is equal to the leg multiplied by the square root of 2.  

This means that x, the hypotenuse of the triangle, is 3√2.