Let x = dealer cost
Marked up price = dealer cost + amount of markup
If the markup is 11% , then x + 0.11x = 26000
1.11x = 26000
x = $23,423.23
If the markup is 18%, then x + 0.18x = 26000
1.18x = 26000
x = $22,033.90
Dealer cost ranges from $22,033.90 to $23,423.23