Do someone could help me solving the following problem

U E C
2'000'000.- 1'000'000.- 5'00'000.- Initial amounts

-20'000 -12'000.- -53'000.- Amounts variation

-1.00% -1.20% -1.06% % in pourcentage


100.00% 120.00% 106.00% poucentage ratio beween
themselves

100.00% 96.00% 98.00% pourcentage ratio wished

-1641.5 (0) (a)1621.5 (b)20 amounts add or
soustracte in order to
.................................................. ........................reach
the wishes ratio

-21641.5 -10378.5 -52980 modified amounts by line above

-1.08% -1.04% -1.06% % gain/loss with modified
variations

100.00% 95.91% 97.92% ratio with the modified
amounts between %


How can I reach the % ratio wished , with changing only the (a) and (b)
amounts which influence the (0) amount with this formula =-(a+b)

My aim is to find a way to automatically calculate (a) and (b) knowing
only the wished ratio and the real ratio betwen % gain / loss

Thanks for your help