How to convert from mol% to wt%?

Jun 2018
so the concentration of molecule A is 0.5% mol. The rest of the molecules are water.

This is calculated by (number of molecules of A / total number of molecules) x 100

More specifically, this is [20 / (20 + 3980)] x 100

We are given that the molecular weight of A is 136 g/mol. I have no idea how to use this to convert into wt%.

Would it be perhaps that I have to assume that I must also add that water is 18 g/mol in the equation?

I still don’t know how to go form here though.

I have looked all over the interent and nothing has helped. I’m really confused as to what the formula is for this conversion. Please help.