I made this graph for you- the red is the 80%, and the green is the leftover 20%.
Formula for the volume not a cone=πr2H. π=3.14. R=12×2=24. H=16. 3.14×24=75.36. 75.36×16=1205.76. ANSWER: 1205.76
For each number,there is a 16 probability of rolling it (so 16 for the 1 and also 16 for the 4)