4. If he should need help, he will call us.

Solution:

This sentence uses 'should' with the present tense to express a polite condition. To omit 'if' and use inversion, we start with 'Should'.

1. Original: If he should need help, he will call us.
2. Inverted: Should he need help, he will call us.

Answer: Should he need help, he will call us.