The balanced chemical equation for the reaction is:
2AgNO3 + CaCl2 --> 2AgCl + Ca(NO3)2
Moles of CaCl2 reacted = conc vol = 0.100 3.00 = 0.300 moles
Reaction ratio between CaCl2 and AgNO3 is 1:2. Hence moles of AgNO3 = 0.300 2 = 0.600 moles
Volume of AgNO3 = moles / conc = 0.600 / 0.100 = 6.00L
Of course the easy shortcut is that because both solutions are the same concentration you could just multiply 3.00 2, however this explanation should reason it out more clearly. Hope I helped you :)
