Decreasing stitches help?

I am knitting an infint hoodie. I am working on the hood. The pattern calls for knit(99st) 5 rows. Proceed in stocking st, dec 1 st each end of needle on 3rd and following alt rows until there are 75 stitches. Do I increase at the begining and end of needle or just end of needle on the 3rd row and the end of the 4th row or what?

Every decrease row will have 2 decreases in it - one at the beginning and one at the end. Now we just need to figure out which rows will be decrease rows.

It says that the first decrease row will be on row 3. And then it says ‘following alt rows’ which basically means every other row.

So you will be decreasing one stitch at the beginning and one stitch at the end of rows 3, 5, 7, 9, etc. until you reach 75 stitches. Going from 99sts to 75sts requires a decrease of 24 stitches total, and since you are decreasing 2 stitches every other row, you will have a grand total of 12 decrease rows. Your last decrease row will be row 25.