Lets assume, Sally has X pound of potatoes in her pantry.
So, 4/3 of the potatoes Sally has in her pantry = 

Now, Sally needs 2/3 pound of potatoes and this 2/3 pound of potatoes is 1/3 pound more than that 

So the representing equation will be: 
 
 
 (subtracting
 (subtracting 
 from both sides)
 from both sides)

 (multiplying both sides by 3)
 (multiplying both sides by 3)
 
 
So, Sally has 
 pound of potatoes in her pantry.
 pound of potatoes in her pantry.