If the sum of a number and one is doubled, the result is three less than  the number. find the number

Let the unknown number be x.

sum of a number and one: x + 1

sum of a number and one is doubled: 2(x + 1)

three less than the number: x - 3

2(x + 1) = x - 3

2x + 2 = x - 3

x + 2 = -3

x = -5

The number is -5.

The answer is 1 because you have to flip the sign when dividing by negative number and 3