Discrete Convolutions VBA

I'm trying to convolve two discrete distributions in excel using VBA. (Discrete Convolutions)

The distributions are presented as follows:

A	B
Number	Probability
0	0.2
1	0.3
2	0.5
Number	Probability
0	0.1
1	0.2
2	0.3
3	0.3
4	0.1

Any ideas?