Pre-Algebra · Superchallenge problem

In a city of square blocks, the "street distance" between $(a,b)$ and $(c,d)$ is $|a-c|+|b-d|$ (you can only travel along horizontal and vertical streets). Find the area of the region of all points $P$ whose street distance to $(0,0)$ plus its street distance to $(6,0)$ is at most $10$.