Salts with nitrates as the anion are generally soluble in water. The question isn’t quite clear: Are we being asked what precipitate would form if these solutions were mixed together? If that’s the case, the reaction would be as follows:
Li3AsO4(aq)+ Fe(NO3)3(aq) → 3LiNO3(aq) + FeAsO4(s).
It is odd that we’re given lithium arsenate dissolved in water to begin with as lithium arsenate should be insoluble. But assuming that it is water-soluble, we can obtain the net ionic equation for the formation of our precipitate:
Fe3+(aq) + [AsO4]3-(aq) → FeAsO4(s).
Our precipitate would be iron(iii) arsenate, FeAsO4.