Question 1159985
x = 'the number'
x^2 is the square of the number 
+3x is three times the number
So x^2 + 3x = 28
   x^2 + 3x - 28 = 0
Factored:
   (x-4)(x+7) = 0
    x-4 = 0
    x = 4
and (x+7) = 0
    x + 7 = 0
    x = -7
The number could be either 4 or -7