Add up the balance of all accounts, apply the rate of the band (from 50% to 5%) and add the fixed amount of the band. Balance of R$ 3,000: 30% is R$ 900, plus R$ 150, total R$ 1,050. Balance of R$ 25,000: 5% is R$ 1,250, plus R$ 2,900, total R$ 4,150.