Mix crushed pretzels, 3 tablespoons sugar and melted margarine. Press into 9X13 pan. Bake 7 minutes at 400 degrees(if glass pan, bake 25 degrees cooler). Blend cream cheese, 1 cup sugar and whipped cream and spread over cooled crust. Dissolve strawberry jello in boiling water and add frozen strawberries. Chill until almost set and pour over cream cheese mixture. Chill all until ready to serve.