Answer:
(100-20-20)/2= 30 feet
Explanation:
If the perimeter is 100 feet, and we know the width is 20 feet, then we start my subtracting 40 from 100. Because perimeter is length + length + width + width, 20 is taken off of 100, twice. That leaves 60 feet for the rest of the length. 60 divided by 2 is 3, so that is the length of the garden.