After the 2nd increase row, you are going to do 6 additional increase rows. You are to space them every 6 rows. Let's call the 2nd increase row Row 6, You will then increase in row 12, 18, 24, 30, 36 and 42. As you accumulate additional stitches, they are to be incorporated into your rib pattern. This is most easily done if you have one selvedge stitch and do your increase immediately after than stitch, since you can then make it a knit or purl, whatever fits into your rib pattern. The same thing can be done at the end of a row.