The Garden Center sells an item that it buys for $$2\mathrm{.}50$ and sells for $$5\mathrm{.}75.$ The addition of $$3\mathrm{.}25$ is an increase of $130\%$ of the cost $($$$3\mathrm{.}25+$$$2\mathrm{.}50).$ The difference between the $($$$3\mathrm{.}25)$ is the gross margin. This is an example of

a$.$ bundling

b$.$ markup pricing

c$.$ flexible pricing

d$.$ break$-$even pricing