Joan wanted to engage a contractor to complete some substantial landscaping and paving work on her property. She obtained a written quotation from Doug, a landscaping contractor. Joan accepted Doug's quotation in writing. When the work was partly completed, Doug complained to Joan that he had under-estimated the cost of the materials required for the work. Doug requested Joan to agree to an increase in the price for the work by $2,000. As Joan did not wish to have to get another contractor to complete the work, she reluctantly agreed verbally to pay Doug the extra $2,000. When the work was completed, Joan paid Doug his originally agreed quotation amount and she refused to pay Doug the extra $2,000. Doug now seeks your advice whether he can successfully sue Joan for the outstanding amount of $2,000. Advise Doug, using cases to support your conclusion. (5 marks) (5 marks + 5 marks = 10 marks for question 2)