Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
Solely from the information you have presented, I cannot give you an accurate response. There are many factors besides pre tax profit which determine the value of a business. The type of business will be a major factor. Other factors will include market place stability/growth/decline, financial strength of the business, and the critical functions and value thereof of the selling owner.. One key to remember is that in a 50/50 owned business, if you are selling to the other owner, the fair market value would require that either of you be willing to either pay or receive this price.
Perhaps the best option for you is to consult with several local business brokers and read through any trade journals for similar businesses for sale.