Joanne sells silk-screened t-shirts at community festivals and craft fairs. her marginal cost to produce one t-shirt is $ 5.50 . her total cost to produce 70 t-shirts is $ 435 comma and she sells them for $9 each. a. find the linear cost function for joanne's t-shirt production. b. how many t-shirts must she produce and sell in order to break even? c. how many t-shirts must she produce and sell to make a profit of $800?