Answer:
The length of the hypotenuse of this triangle is 150√2 mm.
Explanation:
Consider the square ABCD shown in the image below.
The sides are 150 mm each.
All the angles of a square are 90°.
Now The square is folded in half along the diagonal BD.
The angles A, B and D are: 45°, 45° and 90°.
The hypotenuse of the right angled triangle is BD.
Compute the length of BD using the pythagoras theorem as follows:

Thus, the length of the hypotenuse of this triangle is 150√2 mm.