Root Beer Float Cake

1 package (18-1/4 ounces) white cake mix
1-1/4 cups root beer
2 eggs
1/4 cup vegetable oil

Frosting
1 envelope whipped topping mix
1/2 cup chilled root beer

In a mixing bowl, combine the first four ingredients. Beat on low speed for 30 seconds; beat on high for 2 minutes. Pour into a greased 13-in. x 9-in. x 2-in. baking pan. Bake at 350° for 35-40 minutes or until a wooden pick inserted near the center comes out clean.

Cool completely on a wire rack. In another mixing bowl, beat frosting ingredients until stiff peaks form. Frost cake. Chill. Makes 12-15 servings