Increasing stitches

hello
I am trying to make a slouchy hat and right now i have 96 stitches and i have to increase this to 121, which is i have to add 25 more to the last row, what i am having problems with is figuring out do i add a stitch every third or fourth stitch, can someone help me with this please

Welcome to KH!
It’s going to be every 3 or 4 sts (every 3.84sts). Mark off the row in fourths and increase 6 sts in three of the quarters and 7 in one of the quarters. That’ll distribute the increases approximately evenly over the row and help keep you on track.