The square of a negative number is 28 more than three times the negative number

Let the number be x, and remember that x is negative.

Then x^2 = 3x + 28.  Rearranging terms, x^2 - 3x - 28 = 0

Factoring, (x+4)(x-7) = 0.  Solving for x, x=-4 and x=7.  Discard x=7.

The answer is x=-4.

Check:  Is this true for x = -4?

"The square of a negative number is 28 more than three times the negative number."

(-4)^2 = 28 + 3(-4)             or    16 = 28 - 12                 yes, this is true.

21/2 or 5/2