From Förberedande kurs i matematik 1

By moving the term in x over to the right-hand side and dividing by 3, the inequality can be rewritten as

\displaystyle y\le 2-\frac{2}{3}x\,\textrm{.}

Then, we see that the area that we should shade consists of all the points under the straight line \displaystyle y=2-\tfrac{2}{3}x\,.