There are 42 new houses being built in a neighborhood. Last month, 2/3 of them were sold. This month, 3/7 of the remaining houses were sold.

So you start off with 42 houses.

Subtract ((2/3) * 42) first:

$${\mathtt{42}}{\mathtt{\,-\,}}\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}{\mathtt{\,\times\,}}{\mathtt{42}}\right) = {\mathtt{14}}$$

Now subtract ((3/7) * 14):

$${\mathtt{14}}{\mathtt{\,-\,}}\left({\frac{{\mathtt{3}}}{{\mathtt{7}}}}\right){\mathtt{\,\times\,}}\left({\mathtt{14}}\right) = {\mathtt{8}}$$

Final answer: 8 houses:)