What equation means that $7$ less than twice a number is $-1$?

Hint: In this problem we need to find the equation for the given statement. First, we will assume a number as $x$. Now twice of the number is given by multiplying the number with $2$. Now the term $7$ less than can be treated as subtraction of $7$ from the twice of the number. We will convert it mathematically by using appropriate mathematical symbols. In the given statement we have also that the result is equal to $-1$. So, we will equate the obtained expression with $-1$ to get the required result.

Complete step-by-step answer:
Given a statement is, $7$ less than twice a number is $-1$.
Let us assume the number as $x$.
First, we will calculate the twice of the number by multiplying the number with $2$, then the twice of the number is given by $2x$.
Now the $7$ less than twice a number is treated as the subtraction of $7$ from the twice of the number. We have twice the number as $2x$. Now subtracting $7$ from the twice of the number is given by $2x-7$.
In the statement we have that the final result is equal to $-1$. So, equating the above calculated expression which is $2x-7$ with $-1$, then we will get
$2x-7=-1$

Hence the required equation is $2x-7=-1$.

Note: In this problem they have only asked to calculate the equation. So, we have calculated the equation only. In some cases, they will ask to calculate the number also. In that case we need to calculate the solution for the obtained equation.