U. Usman

Department of Mathematics, Usmanu Danfodiyo University, Sokoto, Nigeria

S. A. Yelwa

Department of Environmental Sciences, Federal University Dutse, Jigawa State, Nigeria

S.U. Gulumbe

Department of Mathematics, Usmanu Danfodiyo University, Sokoto, Nigeria

A. Danbaba

Department of Mathematics, Usmanu Danfodiyo University, Sokoto, Nigeria

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