Question

¡Si ___________________ hace un error, posiblemente necesito un sombrero!

Answer 1

To complete the sentence in Spanish you need to say:
¡Si ______El___________ hace un error, posiblemente necesito un sombrero!

The translation of the sentence is:

If he makes an error, I probabbly need a hat. 

Answer 2

If ___________________ makes a mistake, I probably need a hat!