Help translating knitting instructions

I’m knitting sleeves for a baby jumper but can’t understand the following instructions - any knitters able to help me?

Work 28 rows ridge patt as given for back [this I get] at same time incl one st at each end in 5th and foll 6th rows until there are 50 sts.

I’m starting with 42 sts which means I need to add 8 (2 per row x 4), but not sure whether this needs to be in the 5th, 6th, 7th and 8th rows, or 5th, 6th, 12th and 18th - or something else?

Then it says to cont in stocking st incl one st at each end of next and foll 6th row/s until there are 56 sts.

Again, in which rows should I be adding these additional stitches?

5th, 11th, 17th and 23rd. That gives you your requisite 8 extra stitches.

The next time it wants 1st, 7th and 13th.

The “foll 6th” thing just means “count 6 more from wherever you did it last”.

May you have speedy knitting!

ETA: Oh, and I just realised that the first row for the stocking stitch section is 6 rows from row 23 of the ridge. So you really do just keep doing every 6 rows till you’re done.

I agree with the above poster’s interpretation.