Combine postage, how much do I charge?

[NotBoasting]

Someone has just bought 2 sets of clothing from me and wants me to sell her another set that I had listed but she didn't manage to bid for in time. It had no bids so I don't mind selling it to her.

Anyway, any idea how much I should charge for combined postage of all items? There will be 3 t-shirts, 2 pairs of shorts and a pair of jeans (all kids sizes).

Individually I was charging around £1.80 postage for each set.

[Simplysally]

Weigh it all together wrapped for delivery and check on the Royal Mail website for the size/weight. You could always discount that a bit if you wanted.