Let's call p pots and d dishes.
We know that the sets of pots cost $30 and the set of dished cost $20, we express this as the following

Since the target sales are $700.
The total number of pots and dishes people bought were 30 sets, we express this as the following.

We can form a system of equations we these equations.

To solve this, we multiply the second equation by -20, then we sum equations to eliminate d and solve for p.

There were sold 10 sets of pots.
Now, we find the sets of dishes sold.

There were sold 20 sets of dishes.