$1)$ If a supplier offered to provide a rush order of buns at $$1\mathrm{.}00$ a bun, is it worth the money?

$2)$ How will the objective value and optimal solution change if lettuce increase by $1$ lb$?$

$3)$ How will the objective value and optimal solution change if the revenue of Taco changes to $$2?$

$4)$ How will the objective value and optimal solution change if the revenue of Cheese burger reduces to $$1\mathrm{.}5?$

please explain a bit more about the relationship between objective value and allowable increase and decrease