$(6$ points$)$ In town, store A sells Air Garnett's for $$100$ and Ronko Coffee Grinder for $$125.$ Store B$,$ which is $20$ miles away, sells the same products for $$75$ and $$100$ respectively.

a$.(2$ points$)$ What is the expense in conceptual terms$)$ of Joe Blow going to store $B?$

He has to drive $20$ minutes away.

b$.(2$ points$)$ What is the opportunity cost $($in conceptual terms$)$ of Joe Blow going to store $B?$