There is no single number that satisfies those conditions.
It can't be one. Mixed numbers are greater than one (less than negative one).
In words, the same idea could be expressed as: "Six less than a number is negative fifteen".
Less than negative 11
Negative a is greater than, equal to or less than 0 depending on whether a, itself, is less than, equal to or greater than 0.
Negative seven is greater than negative seventy.
Negative 163 is less than negative 5.30 is.
It is less than -3.
Negative 5 is less than negative 4.
-4 is greater than -8.