Use a value from another table in a formula field


I would like to use a parameter in a formula.

Some context:
I have a table A with different rates for each rows. (rate1, rate2, rate3).
I have a table B with weighs for each of the rate (rate1_weigh = 1, rate2_weigh = 2, rate3_weigh = 5)

I want to calculate the overall rate for each rows using weighs for each rate.
Something like:
(rate1_weigh * rate1 + rate2_weigh * rate2 + rate3_weigh * rate3) / (rate1_weigh + rate2_weigh +rate3_weigh)

How could I call the weigh that I have in table B in the formula I write in table A?

Thanks a lot for your help,