what is legal issueLegal test argument for plaintiff and defendant

Jane owns a hair salon. Maggie has business selling hair products. Jane and Maggie entered into a contract for the supply of 20 large shampoo and 20 large conditioner at a price of $10 a bottle or a total of $400. Later Jane was in a local store and saw the same product on sale for $8 per bottle which would be a total of $320, that is, $80 less. Jane telephoned Maggie and told her. Maggie agreed that Jane could pay $8 per bottle. Maggie delivered the 40 bottles and invoiced Jane for $400. Heather sent a cheque for $320 and Maggie sued for payment of the $80 difference. 1. What is the legal issue/question? (2 marks) 2. What is the rule of law/legal test that applies? (1 mark) 3. Create an argument for the Plaintiff, Maggie (1 mark) 4. Create an argument for the Defendant, Jane (1 mark)