The mathematical translation of "The sum of a number and 7 is equal to 15" is:

$x + 7 = 15$

Where $x$ represents the unknown number.

Would you like further explanation or have any other questions?

Here are five related questions:

1. How do you solve for $x$ in $x + 7 = 15$?
2. What happens if you change 7 to another number?
3. How can you represent "the difference of a number and 7" in mathematical form?
4. How do you represent "twice a number is equal to 20" in symbols?
5. How can this equation be graphically represented?

Tip: When translating word problems to equations, always identify key terms like "sum," "difference," "product," and "quotient" for correct operations.