Cast on 15 stitches in the red on a size 10 needle.
Knit in garter stitch for twenty-ish rows (until it looks the way you think it should).
Switch to yellow and size 8 needles for two rows.
Fours rows red on size 10.
Two rows yellow on size 8.
Repeat from beginning, checking length of red section against original red section until scarf measures 5ft.