Luther and his dad are in charge of ordering t-shirts for the father's day 5k fun run. they order a large number of t-shirts from a website that allows luther to upload his own design. when the shirts arrive, luther discovers that 40 of the shirts have the wrong design! now luther and his dad only have 160 usable t-shirts. which equation can you use to find the total number of t-shirts ⁿ in the order?