Find all real values of s such that x^2 + sx + 144 - 140 is the square of a binomial.

The polynomial is just x^2 + sx + 4. For the polynomial to be the square of a binomial, the discriminant is equal to 0.

\(s^2 - 4(1)(4) = 0\\ s^2 = 16\\ s = \pm 4\)