Determining Opportunity Cost?

The confutations to appropriate from are: $45, $60, $30 & $15 for the primary utter and her topical line garner, the shop athwart town, or the garner in the nigh city. I do not discern how we are deemed to obstruct in the #s to get the confutations for the primary one and then to get the confutation for the cooperate off of the foregoing confutation.