In this paper, a mathematical model was proposed to deal with the …

• Abstract
• Background
• Methods
• Results and Discussion
• Conclusion
• Authors' Contribution
• Appendix
• Acknowledgements
• References
• Tables

One of the authors (A.B) is grateful to the British Council (Morocco) for financial support during the period of research. This paper is dedicated to Wiam Boutayeb and David M. Barlett.