The density of solid AgCl is 5.56 g/cc.Solid is arranged in cubic aray of Ag= & cl- ions spaced at a distance of 2773 Armstrong.With this find Avogadro constant.

Let's clean up loose ends.
This is a number crunching problem so get out your calculator.
You are given the density of AgCl; your periodic table gives you the information to calculate the number of moles in a cc of AgCl. Fact one.
The crystal is an assembly of tiny cubes of the given dimensions. From this you can calculate the volume of the unit cubes. Fact two.
Division gives yoou the number of cubes in a cc of AgCl, from this you get the number of cells (ions) in a cc. This gives you the number of ions in a mole.
Now for the real problems:
1. What is an "Armstrong?" I'll bet you mean an Ångström Unit.
2. Nearly 3000 Ångströms sounds way to big for a cell dimension.
Check the original problem. Crunch the numbers.
You probably needed this last week but maybe this will help.