(X^2+8X+3)(X^2+8X+4)=0

Since the product of these two sets of brackets is zero, then either of them could be zero.  They each contain a quadratic, so use the quadratic formula to find the corresponding values of X.

 

For the first the two possible values of X are given by:  X = (-8 ± √(8² - 4*1*3) )/2

 

For the second:  X = (-8 ± √(8² - 4*1*4) )/2