$$d = \sqrt{(3.00 \text{ blocks west} + 6.00 \text{ blocks east})^2 + (4.00 \text{ blocks north})^2}$$
$$d = \sqrt{(-3.00 + 6.00)^2 + (4.00)^2}$$
$$d = \sqrt{9.00 + 16.00}$$
$$d = \sqrt{25.00}$$
$$d = 5.00 \text{ blocks}$$
Therefore, the displacement is 5.00 blocks at an angle of 53.1° north of east.