please help me how to solve this in AMPL ad how to formulate the model
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This forum is not an appropriate place to post an entire exercise, or to ask for general help getting started with an AMPL assignment. However if you have a specific question about using AMPL, such as how to write a certain constraint, or interpret a particular error message, or use a particular solver, then you can post your question here. Be sure to include a copy of the AMPL statements that you have already written (or attach your model and data files) and provide the full text of any error messages that you are seeing.
I see that you separately posted an AMPL model, so you should also look for the reply to that.