HVAC Supplies, Incorporated $($HVAC Supplies$)$ has assured $68$ Degrees Heating and Air Conditioning, LLC $(68$ Degrees$)$ in writing that it will provide $45$ HVAC units of a designated model at a price of $$4,500$ for each unit. This assurance will last for $30$ days. HVAC Supplies has made $68$ Degrees which of the following?