Seeking A Formula Instead Of Having To Use Goal Seek?

Say employee John Doe has a salary X. Giving him a salary raise Y (euro/dollar) induces a pension premium to be paid by the employer, on that amount.

The premium is (fixed) 17% of the part above a (fixed) treshold value of 3.750. On the part of the raise below the 3.750, the pension premium is (fixed) 4,35%.

E.g. having a salary of 3.600, with a raise of 400.
4,35% of (3.750 - 3.600 = 150) equals 6,525
And 17% of the remaining 250 equals 42,500
So the total premium is 49,025

But, I want to give a raise with a total cost of no more than 400. So, I use goal seek to find a raise that, together with te pension premiums equals 400.

In the example, with 3.600 as a salary to start with, that raise would be 358,10 Because the part below 3.750 stays the same and induces a premium of 4,35% of 150, being 6,525 and the remaining part is 208,10 at 17% is 35,377.

Proof: 358,10 + 6,525 + 35,377 = 400

The question is: is there a possibility to have a formula that calculates the (e.g.) 358,10 based on a salary to start with (e.g. 3.600), an aimed total cost (e.g. 400) and the fixed constants 3.750, 17% and 4,35%?