Hint: We have to write the given word phrase into algebraic expression form. To convert the given word phrase into a variable expression we will first assume a variable x. Then we convert each word into variable and operator.
Complete step-by-step answer: We have been given a word phrase “Twice the quantity a number and 3. We have to convert the word phrase into a variable expression. We know that a variable expression is the combination of numbers, variables and operational symbols. Let us first assume that the number is x. First let us interpret the line a number and 3. Then we will get $\Rightarrow x+3$ Now, we know that twice the quantity means that we need to multiply the obtained quantity by 2. Then we will get \[\Rightarrow 2\left( x+3 \right)\] So we get the variable expression as \[2\left( x+3 \right)\] for the given word phrase.
Note: It is necessary to add parenthesis in the given expression as we have to find the twice of the whole quantity. Students may misinterpret the given word phrase and write the expression for the line Twice the quantity a number and 3 as $2x+3$. Another mistake students can make is that they convert the word ‘and’ as multiplication and write the expression for the line a number and 3 as $3x$, which gives the incorrect answer. So it is necessary to understand the meaning of each word before converting.