The length and width of the garden are 93 feet and 62 feet respectively. 
<u><em>Explanation</em></u>
Suppose, the length of the rectangular garden is  feet.
 feet. 
As the width is exactly two-thirds of the length, so the width of the garden will be:  feet.
 feet. 
310 feet of antique picket fencing are to be used to enclose the garden. It means, <u>the perimeter of the garden is 310 feet</u>. 
<u>Formula for perimeter of rectangle</u>  
 
So, the equation will be....

So, the length of the garden is 93 feet and the width is  feet.
 feet.