Theodore's total earnings from the stone statues are 10 x $20 = $<<10*20=200>>200.
His total earnings from wooden statues are 20 x $5 = $<<20*5=100>>100.
So his total earnings from the stone and wooden statue are $200 + $100 = $<<200+100=300>>300.
The amount he pays for the tax is $300 x 10/100 = $<<300*10/100=30>>30.
Therefore his total monthly earnings are $300 - $30 = $<<300-30=270>>270.
#### 270