Cracking the Code: Algebra Expressions

Imagine a machine. You drop a number in. The machine triples it and adds 4, then spits the result out. If you drop in 2, you get 10. If you drop in 5, you get 19. If you drop in 0, you get 4. Here is the puzzle: can you write a single rule — using a letter for any number you drop in — that describes what this machine always does? That one rule is an algebraic expression, and by the end of this lesson you will write it yourself.