Hello, Camila,
The definiton of Molar is moles/liter. A 1 molar solution will have one mole of solute per 1 loter of solvent. In this case, we want 5.0 liters of 5.0 Molar soultion That means we would need 5*(5moles/Liter) or 25 moles of silver nitrate. That makes 5 moles per liter, or 5.0 Molar.
Bob