I need to make a "40" number birthday cake for a 40th birthday party serving 45 guests. How should I calculate the size of the sheet cake that I will have to bake to carve out the numbers 4 and 0 and serve 45 guests. Its a 2 layer chocolate cake with woth mocha fillng.. Please guide I AM stuck.

AThere might be an easier answer to this (I hope there is!) but when I need to make a special shape like this I draw it out on graph paper, allotting 2"/square. I draw it large enough to provide the right number of servings. (Some old high school area calculation comes in here, breaking down the diagram into smaller shapes and adding up the area of each.) I count out how many squares down and across the total shape takes up, and then I know how large a cake I need to start with. Hope that makes sense. If it doesn't, I can try to do a diagram for you. :)