Answer:
C. √55.
Step-by-step explanation:
The vertical line cuts the base of the triangle in 2 so the right angled triangles both have a base 3 cm long.
So by Pythagoras:
8^2 = x^2 + 3^2
x^2 = 8^2 - 3^2
x^2 = 55
x = √55.
