Given,

28 – 31x – 5x²

Now first find the numbers whose-

Sum = - 31 and

Product = - 5 × 28 = 140

Required numbers are 35 and 4,

So we get;

28 – 31x – 5x²

= 28 + 4x – 35x – 5x²

= 4(7 + x) – 5x(7 + x)

= (7 + x)(4 – 5x)