A=39cm2 h= ? They give you the base which is 13 cm.

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Think of your rectangle. One side times the other side equals your area. So, the height X base = area. Just plug in your values which would lead you to divide your area (39 cm²) by the one side you know the length of (your base = 13 cm). Your height will then equal whatever 39 cm² / 13 cm is. (Note: remember to include your units in your calculations so that don't end up with a side that is n cm² long or something, because that would just not make sense (-; ). I hope this helps :-)