CB is 10.392...
(root 12^2 - 6^2 = 6root3)
CB is now the opposite
CD = hypotenuse
Hypotenuse + opposite = SOH - sin
Sin55 = o/h
sin55 = 6root3/h
x h, then ÷ sin55
H = 6root3/sin55
H = 12.686...
To 3 s.f CD is 12.7cm
(root = square root)
Hope this helps!