By symmetry, the red vertical line measures 4 cm. On the other hand, the red horizontal line measures 5 - 3 = 2 cm.
Notice that the line segments that measure 2 cm, 4 cm, and form a right triangle wherein is the hypotenuse of the right triangle. So by Pythagorean Theorem, we find that
Answers & Comments
The answer is D. 2√5 cm.
See attached file.
By symmetry, the red vertical line measures 4 cm. On the other hand, the red horizontal line measures 5 - 3 = 2 cm.
Notice that the line segments that measure 2 cm, 4 cm, and
form a right triangle wherein 
is the hypotenuse of the right triangle. So by Pythagorean Theorem, we find that
Solving for
yields 
.