a. Determine if exactly six squares of the 3 by 3 grid shown can be shaded so that no thre...

a. Determine if exactly six squares of the 3 by 3 grid shown can be shaded so that no three shaded squares line up horizontally, vertically, or diagonally.

---

b. Determine if exactly 12 squares of a 4 by 4 grid can be shaded so that no four shaded squares line up horizontally, vertically, or diagonally.