I am currently confronted with a bonus participation scheme problem as
follows:

Assumptions:
Column B4:B13 Names of 10 employees Employee1:Employee10
Column C4:C13 Annual salary of each afore-mentioned employee
Cell C1 = Average Bonus-Amount of 2.5% of the total annual salaries
(SUM(C4:C13)/100*2.5)
Column D4:D13 Individual Performance Assessment rating from 0.0
(minimum) to 4.0 (maximum)
Column F4:F13 Individual Bonus-Amount as a percentage rate
Column G4:G13 Individual Bonus-Amount
Cell G15 = Cell C1 (i.e. SUM(G4:G13) = C1)

Depending on the individual performance assessment, a bonus factor
must be applied in order to calculate an exponentially increasing
individual bonus amount, e.g.

Assessment - Bonus-Amount as a percentage of the annual salary

B19 = 0.0 - C19 = 0.00%
B20 = 1.0 - C20 = 0.63%
B21 = 2.0 - C21 = 1.56%
B22 = 3.0 - C22 = 2.81%
B23 = 4.0 - C23 = 5.00%

Restrictions: The total average bonus amount must be 2.5% of the total
annual salaries, see above Cell G15.

How can I make use of the GOAL SEEK function in order to
a) vary the percentage rates above (C19:C23) AND
b) restrict the total amount of bonus to 2.5% (C1=G15)?

Many thanks for any ideas in this respect!