Evaluate 𝑦 minus four, given that 𝑦 equals nine.
Our expression says 𝑦 minus four, but our problem tells us that 𝑦 is equal to nine. We replace the 𝑦 with the number nine. The rest of the expression stays the same. Now, we have nine minus four equals five. If 𝑦 equals nine, the expression 𝑦 minus four equals five.