Let the weight of B to be added to A be x grams, then there is the following equivalence relation:

0. 17×85+0.40×x = 0.35×(85+x)

Among them, the left is the total amount of component A in the mixture of Party A and Party B, and the right is the total amount of component A in the mixture, which should be equal.

Simplifying the above equation, we can get:

0.40 x-0.35 x = 0.35×85-0. 17×85

Namely:

0.05x = 0. 18×85

Solution:

x = (0. 18×85) / 0.05 ≈ 306

Therefore, it is necessary to add 306 grams of B to A to make the content of component A in A reach 35%.