How the spacing is worked out
To add 6 stitches to 24, the round splits into 6 equal sections of 4 stitches. Each section is 3 plain stitches and one stitch worked twice: (1 dc in each of next 3 sts, 2 dc in next st) 6 times, giving 30. When the numbers don’t divide evenly, some sections get one extra plain stitch, and the instruction lists those first.
Decreases work the same way with a two-together: 30 down to 24 is (1 dc in each of next 3 sts, dc2tog) 6 times.
Tips
On flat circles and hats, start each round’s first section at a different point, or the increases stack into corners. One increase per stitch is the most a single round can take; more than that, or a decrease of more than one in two, needs two rounds or a three-stitch decrease. The written round uses UK terms: switch with the US to UK converter if your pattern is American.