Orange-Blueberry Streusel Cake
["1/4 c. sugar", "2 Tbsp. all-purpose flour", "2 tsp. grated fresh orange rind", "1/2 tsp. ground cinnamon", "1 Tbsp. margarine", "1 (16.5 oz.) box light 97% fat-free wild blueberry muffin mix", "3/4 c. fresh orange juice", "1 tsp. vanilla extract", "1 egg white"]
["Combine sugar and next 3 ingredients in a bowl; cut in margarine with a pastry blender until mixture resembles coarse meal.", "Set aside."]
["sugar", "flour", "orange rind", "ground cinnamon", "margarine", "muffin mix", "orange juice", "vanilla extract", "egg"]