4.25mm hook

American Half-Treble Crochet Stitch (htr)
htr =
“Yo twice. Insert hook in next stitch and draw up a loop (4 loops on hook)
Yo and draw through two loops (3 loops on hook)
Yo and draw through remaining loop (1 loop on hook))

I marked the ch-2 corner spaces on Rs 7 & 8