Increase help

Hi there! I need some help deciding which increase I need to use. The instructions are as follows: p4, [inc in next st, p1]21, p4.

Should I use the M1F, M1B, Kfb? Thank you very much.

When a pattern says to increase [B]in[/B] a stitch, you would use kfb. The other increases are done between stitches.

Thank you very much! Exactly what I needed to know.