Anumber is multiplied by 12 that tree is added to the result if the number is 51 what is the original number

Pls , the question is in the picture!

Amuffin recipe, which yields 12 muffins, calls for cup of milk for every 1 cups of flour. the same recipe calls for cup of coconut for every cup of chopped apple. to yield a batch of 30 muffins, how much flour will be needed in the mix?

Explain how you do each step what term makes it inconsistent y=2x - 4 ?