Each new car in the lot at Rollway Motors costs more than $18,000.
Conclusion
Costs $5 - $18 → used < 10 yrs. old
Evidence
New → costs > $18
≥ 10 yrs old → costs < $5
Evaluate
This conclusion takes the contrapositive of each rule to derive the upper and lower boundary of its conclusion.
If it costs < $18, then it's not new (i.e. Used). If it costs > $5, then it's less than 10 yrs old.
Thus, if it's between $5 - 18, then it's got to be Used and less than 10 yrs. old.
Goal
The argument needs to give us two conditional premises. The conclusion's trigger should be the net effect of being "Not outcome 1 + Not outcome 2".
The premises' outcomes were → more than $18. → less than $5
And the conclusion's trigger was between $5 and $18.
The outcome of the conclusion should combine the negation of the two triggers. The premises' triggers were New → 10 or more yrs old →
So the conclusion's outcome was Used and less than 10 yrs old