# How do you translate "double the difference of a number and seven" into a mathematical expression?

If $x$ represents "a number", then the mathematical expression you want is $2 \left(x - 7\right) = 2 x - 14$.
The difference of the number $x$ and $7$ is $x - 7$. Doubling this means to multiply it by 2 to get $2 \left(x - 7\right)$. If you want, you can expand this, by the distributive law, to get $2 x - 14$.