Question

grams of CaO that form when 20g Ca burn: 2Ca+ O2---2CaO

Answer 1

assuming there's excess oxygen, you should convert your grams of calcium to moles using molar mass. (this is done by dividing mass by molar mass) then use dimensional analysis to find how many moles of calcium oxide would be formed. (use a ratio of moles calcium to moles calcium oxide) from the moles, convert to grams by multiplying by the molar mass. (You should become familiar with converting between grams and moles)