The person will pay 120 reais minus the discount which is $30\%$ of 120. That is: $120-0.3 \times 120=120-36=84$ reais.
2- We can also solve this problem by noting that if the discount is $30 \%$, then the price the person will pay is $70 \%$ of 120, that is: $0.7 \times 120=84$ reais.