2017 AMC 10A Problem 3

Find the dimensions of the whole rectangular garden including walkways

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

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.