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Most studies on chemical enrichment in galaxies focus on the gas and stellar metallicities separately, including studies on radial metallicity profiles of local galaxies using IFU data. A negative gradient in gas and stellar metallicity is found to be prevalent in nearby galaxies. The negative gas or stellar metallicity gradient can be reproduced by chemical evolution models with radial dependent gas accretion. However, few studies directly compare the observed gas and stellar metallicities. The stellar metallicity carries information about the early epochs of chemical enrichment in galaxies and is therefore a crucial observable to constrain the formation of galaxies. Gas metallicity, instead, reflects more recent evolution processes. In this project, we select a sample of star-forming galaxies observed by the MaNGA survey and study the origin of the gas and stellar metallicity gradients of star-forming galaxies by comparing with predictions from a chemical evolution model. Our results show that only two scenarios are capable of reproducing the gas and stellar metallicity radial profiles simultaneously. One scenario invokes a time-dependent metal outflow rate with high rates at early times. The other viable scenario uses a time-dependent IMF slope, in which a steep IMF slope is needed at early times.