What's a good price for a 2013 Kia Optima SX with 20k miles?

Looking at 2 different Kia Optima's both used
1.) 2013 Kia Optima SX for $18,700 with 20k in miles
2.) 2013 Kia Optima EX for $17,500 with 15k miles
1.) 2013 Kia Optima SX for $18,700 with 20k in miles
2.) 2013 Kia Optima EX for $17,500 with 15k miles
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