The actor's neck is 20.08 cm long.
Step-by-step explanation:
The actor who plays Captain Terrific on television is 216 cm tall. Miguel’s doll is 10 cm tall.
Miguel’s doll is 10 cm tall and the doll’s neck is 0.93 cm long.
Let the doll's actor's neck be x cm
We can relate these as follows:

Solving for x now;

=> 
x = 20.08
Hence, the actor's neck is 20.08 cm long.