59.99 - 59.99 x saving rate = 42.89
with saving rate = r%
59.99 - 59.99 x r% = 42.89
so 59,99 ( 1 - r%) = 42.89
1 - r% = 42.89 : 59.99
1 - r% = 0,7150
r% = 1 - 0,7150
r = 28,5%
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