Answer: B

Small Hint:

Find the dimensions of the whole rectangular garden including walkways

Big Hint:

Subtract the total area of the six flower beds from the outside rectangle

Solution:

We can see that the width of the garden is $$2 \cdot 6 + 3 \cdot 1 = 15.$$ We can also see that the height is $$3 \cdot 2 + 4 \cdot 1 = 10.$$ The total area of the garden is therefore $15 \cdot 10 = 150.$ The area of all the flower beds is $$6 \cdot 2 \cdot 6 = 72.$$ Subtracting this from the area of the garden yields $150 - 72 = 78,$ which is the area of the walkways.

Thus, B is the correct answer.