Alhaji - any approach/methodology requires justification. For me, the main justification for using a mixed methods approach is that a broad over-arching question can only be answered by using more than one methodology. In doing so, the process is more likely to be pragmatic and transformative and, therefore, result in multiple, practical outcomes.
The attached chapter really assisted me sir. I am grateful for your guide. I also learnt from this guide you sent that mixed method can be used as a complement data.
The use of mixed methods is partially justified by the fact that by themselves the qualitative and quantitative components could not answer your research question. However, and in a very interesting (and sometimes unforeseen) way, the use of mixed methods produces results in a synergetic way, which do not arise in qualitative or quantitative research on their own.