Eight is added to a number and the sum is doubled, the result is -11 less than the number. Find
the number

If you don’t know what a number is, you should substitute it for x and make an equation with the information you have been given. This gives:

(x + 8) x 2 = x - 11

Then, solve:

2x + 16 = x - 11

2x = x -27

x = -27

This can then be checked by using the number in the original text.

-27 + 8 = -19

-19 x 2 = -38

-38 is 11 less than -27.

Hope this helps :)