12. Mario is making chocolate cakes. For each cup of milk he uses, he needs to use \( 1 \frac{3}{4} \) cups of flour. For each cup of flour he uses, he needs to use \( \frac{3}{7} \) cup of cocoa powder. Mario is making enough cakes that he needs to use 4 cups of milk. How many cups of cocoa powder does Mario need to use?

To find out how many cups of cocoa powder Mario needs, we first determine how much flour he will use. For 4 cups of milk, he needs: \[ 4 \text{ cups of milk} \times \frac{7}{4} \text{ cups of flour per cup of milk} = 7 \text{ cups of flour} \] Next, to find the amount of cocoa powder for 7 cups of flour, we use the ratio \( \frac{3}{7} \) cup of cocoa powder per cup of flour: \[ 7 \text{ cups of flour} \times \frac{3}{7} \text{ cup of cocoa powder per cup of flour} = 3 \text{ cups of cocoa powder} \] So, Mario needs 3 cups of cocoa powder for his cakes.