UOM of products

[Hoan dang van]

Hi all
I want to create a products that have more two uom ( A and B ...). B
is basically UOM has price is 5$ and is default uom when sale product, A
is extendedly UOM ( A = 50B) has price is 245$ and is default uom when
purchasing or receipt product.
Can everybody show me how this dose.
Thank all