I usually do everything in moles:
1. convert 72g AgCl into moles = 72g/(144g/mol) = 0.5 mol
2. since there is one mole of calcium chloride needed to produce 2 moles of silver chloride, you just divide by 2 to give your moles of calcium chloride. 0.25 mol CaCl2 (if the question was the other way around you would multiply by 2)
3. molar mass of CaCl2 = 110g/mol
4. in order to just get grams, you need to get rid of the mol so you multiply 110g/mol * 0.25mol = 27.5 g of CaCl2
I find that when doing calculations like these, keeping your units help. This is just another explanation to the problem. The previous poster's method is perfectly feasible.