A cake recipe requires 3 1/4cups of flour for 13 servings and 4 1/2 cups of flour for 18 servings. How much flour is required to make a cake that serves 28 ?

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Kimmai -This is a "proportion" or ratio problem.For example, if you need 1 cup of flour for 4 servings, you would double the flour for 8 servings, right?  Using proportions you would set it up like this:So, solving for x, you would need 2 cups or double for 8 servings.Now set up the problem you have:Now, just solve for x like the example above.Hope this helps