I don't agree with salmonmac that you put the new st back on the L needle, you don't mess with the new sts at all.
Just k3tog, leave that st on the L needle, yo, knit into the same sts again, yo, knit into the same st again. That will give you 5 sts on the R needle and you can let the k3tog sts off the L needle. Then go on to the next st and purl the 5 sts separately on the next row.
For the other one, k2tog, yo, knit into the same sts again and there's your 3 sts. You might want to practice this with some other yarn and a really large needle to keep the sts loose.