Math
posted by Cherie .
Tracy made a stained glass jewellery box. It measured 20cm by 12cm by 8cm.
a) About how much glass did Tracy use?
b) one piece of glass has an area of 100 cm squared and costs $3.65. How much did the glass cost?(assume all pieces can be used
Please help don't understand this!!!

First find the surface area of this rectangular prism.
Surface Area of a Rectangular Prism = 2ab + 2bc + 2ac
http://www.math.com/tables/geometry/surfareas.htm