Let's first add some lines to divide the walkway into 4 rectangular regions (A, B, C and D), and then find the area of each region.
We'll start with region A.
Since the walkway is uniformly 3 feet wide, we can add this to our diagram.
We'll also add the fact that the garden is 18 feet long.
At this point, we can see that the total length of region A = 18 + 3 + 3 =
24 feetSo, the area of region A = (3)(24) = 72
Since region B is identical to region A, we know that the area of region B = 72 also
Now let's examine region C.
We can see that the dimensions of region C are 3 by 12
So, the area of region C = (3)(12) = 36
Since region D is identical to region C, we know that the area of region D = 36 also
TOTAL AREA of walkway = 72 + 72 + 36 + 36 = 216
Answer: 216