Please have a complete and well explain answer !! I will upvote

The Bander Company was seeking an accountant. Eber & Fowler (E&F), an accounting firm, offered to prepare financial statements, provide ongoing advise, and do an audit for an annual fee of $3500.00. The Bander Company responded that the price was too high. E&F submitted a new proposal for $3000.00. The Bander Company then hired E&F for $3000.00. During the first year of the contract, the financial statements took longer to prepare than E&F had anticipated. E&F therefore charged Bander $3400.00 for the first year. Bander refused to pay.

Question: If E&F sues Bander Banner for the $400.00, what is the likelihood of success? Why?