help me please i need it rn

[tex] \rm \: this \: month, \: Mikasa \: earned \: only \rm \frac{-3}{4} \:of \: his \: earning \: last \: month\: if \: his \: earning \: last \: month \: is \: 12,600 \: how \: much \: did \: he \: earn \: this \: month[/tex]