Question 76366
First, factor out a common factor of the coefficients:

{{{5x(4x^2+12x+9)}}}

Working on the inside of the parentheses, what two numbers when added equal 12 and when multiplied equal 36(because 4*9=36). 6 and 6

{{{5x(4x^2+6x+6x+9)}}}

{{{5x((2x(2x+3)+3(2x+3)))}}}

{{{5x(2x+3)(2x+3)}}}

{{{5x(2x+3)^2}}}