"The sum of" two quantities means you should be using addition. Which two parts are being added in the phrase "the sum of twice a number k and 11"?

In an equation made from words, what mathematical symbol does the word "is" usually stand for, especially in a sentence like "___ is 39"?

For each answer choice, type the equation into Desmos, but use $x$ instead of $k$. Enter each choice’s equation on its own line so Desmos can work with it.

Use Desmos’s solve feature (or graph each side as separate functions and find their intersection) to see what value of $x$ makes each equation true.

For each solution you get, double that value and add 11 (for example, calculate 2*(solution) + 11 in Desmos). The equation that correctly represents the word problem will give a result of 39 when you do this.

The phrase "a number k" means we are using $k$ to represent an unknown number. The phrase "twice a number k" means $2$ times that number, so it becomes $2k$.

The phrase "the sum of twice a number k and 11" means we are adding $2k$ and $11$, so that part becomes $2k + 11$.

The word "is" in a word problem usually translates to an equals sign, so "is 39" becomes $= 39$.

Putting everything together:

• "twice a number k" $\rightarrow 2k$
• "the sum of twice a number k and 11" $\rightarrow 2k + 11$
• "is 39" $\rightarrow = 39$

So the equation is $2k + 11 = 39$, which corresponds to choice C.