A10ft by 20ft rectangular swimming pool is surrounded by a walkway of uniform width. if the total area of the walkway is 216ft^2 , how wide is the walkway?

check the picture below.

so, we know the dimensions of the pool, is a 20x10, so its area is simply 200 ft², and we know the walkway is 216 ft², so the whole thing, including pool and walkway is really 200 + 216 ft².

now, as you see in the picture, the dimensions for the combined area is 20+2x and 10+2x, since the walkway is "x" long, therefore,

notice, it cannot be -18, since is a positive length unit.

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step-by-step explanation: