When you have a polynomial, the multiplicative factors in each term are called its coefficients.
The expressions you have are binomials (polynomials with two terms), and each have two coefficients: 4x+8 has coefficients 4 and 8; -3x-27 has coefficients -3 and -27.
Since there is more than a single coefficient, I think you are asking how to factor these expressions so that the leading coefficient (the coefficient of the term with the highest power) of the binomial is 1.
Consider the binomial 5x-15. I can factor 5 out of the expression by dividing each term by 5:
5x-15 = 5 (x - 3) (Ask yourself why I picked "5".)
The leading coefficient on the binomial after factoring 5 out of the expression is 1.