To express the relationship between the numbers $d$, $e$, and $f$ given in the problem statement, we translate the sentence into a mathematical equation.

The problem states:

"A number $d$ is equal to three times the sum of two numbers $e$ and $f$."

Mathematically, this can be written as:

$d = 3 \times (e + f)$

or more simply:

$d = 3(e + f)$

Explanation:

1. Sum of $e$ and $f$: The expression $e + f$ represents the sum of the two numbers $e$ and $f$.
2. Three times the sum: The expression $3(e + f)$ indicates that the sum $e + f$ is multiplied by 3.
3. Equal to $d$: The whole expression is equal to $d$.

This equation represents the relationship described in the problem.

Would you like to explore more details or have any questions about this? Here are some related questions for further practice:

1. If $e = 4$ and $f = 5$, what is the value of $d$?
2. If $d = 30$ and $f = 4$, what is the value of $e$?
3. How would the equation change if $d$ was equal to two times the sum of $e$ and $f$?
4. If $d = 3(e + f)$, and $e = f$, how would you express $d$ in terms of $e$ only?
5. If $d = 3(e + f)$ and $d = 18$, what are possible values for $e$ and $f$?

Tip: Always remember to distribute multiplication over addition when solving equations involving sums and products.