We know that a rectangle has the top and bottom sides with the same length.
We also know that the left and right sides have the same length.
We know that the distance from G to H is 4
Why?
G is at 1 1/3 and H is at 5 1/3 so the length is 4
The length for F to J must also be 4
Since F is at 1 1/3 we add 4 so 1 1/3 + 4 = 5 1/3
We now know the x value
Lets find the y value by looking at the up and down length.
The length from F to G is 4 2/3 to 2 1/3 = 2 1/3
This must be the same length for J to H
H is at 2 1/3 so we add 2 1/3 to this value
2 1/3 + 2 1/3 = 4 2/3
This is the y value of the coordinate of J
The coordinate of J is ( 5 1/3 , 4 2/3)