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 :)
