If you would like to know the dimensions of the garden, you can calculate this using the following steps:
length ... (2 * x - 4) feet
width ... x feet
area ... 170 ft^2
area = length * width
170 = (2 * x - 4) * x
170 = 2 * x * x - 4 * x
170 = 2 * x^2 - 4 * x
0 = 2 * x^2 - 4 * x - 170 /2
0 = x^2 - 2 * x - 85
1. x = 1 - sqrt(86) = -8.27
2. x = 1 + sqrt(86) = 10.27
length: 2 * x - 4 = 2 * 10.27 - 4 = 16.54 feet
width: x = 10.27 feet
The dimensions of the garden are 16.54 feet and 10.27 feet.