Question

1kg custa 30 reais quanto custa 70g

Answer 1

regra de 3
    
    1 kg --- 1000 g
       y   ---  70 g

y = 70/1000 = 0,07 kg

 
    1 kg --- 30 R$
0,07 kg --- x

x = 2,1 = 2,10 R$

(2 reais e 10 centavos)