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  Add the expressions 14x + 10y - 12xy - 13, 18 - 7x - 10y + 8xy, 4xy.

To simplify the expressions you provided, we can combine like terms and rearrange them. Here are the expressions you mentioned:

• 14x + 10y - 12xy - 13
• 18 - 7x - 10y + 8xy
• 4xy

Now, let's look at each expression:

• For the first expression, we have: 14x + 10y - 12xy - 13. This is already simplified.
• The second expression is: 18 - 7x - 10y + 8xy. This is also in its simplest form.
• The third expression is simply: 4xy.

These expressions cannot be simplified further without specific values for x and y. If you have any particular values for these variables, we can substitute them in to find numerical results.