The equation representing the sentence is:

$5(x + 3) = 12$

This equation expresses that the product of 5 and the sum of a number $x$ and 3 equals 12.

Would you like more details or have any questions about this equation?

Here are 5 related questions:

1. How do you solve the equation $5(x + 3) = 12$ for $x$?
2. What happens to the equation if the product is changed to 15 instead of 12?
3. How would the equation change if the number 3 is replaced with another variable, say $y$?
4. What is the significance of the distributive property in solving the equation $5(x + 3) = 12$?
5. How can you graph the equation $5(x + 3) = 12$ on a coordinate plane?

Tip: When translating word problems into equations, identify key phrases like "the sum of" or "the product of" to determine the mathematical operations involved.