Question 153541
I'm assuming your first = sign is actually a - sign. 

Here you go:

x^(2)+4x+8-8x=29

Since 4x and -8x are like terms, add -8x to 4x to get -4x.
x^(2)-4x+8=29

Since 8 does not contain the variable to solve for, move it to the right-hand side of the equation by subtracting 8 from both sides.
x^(2)-4x=-8+29

Add 29 to -8 to get 21.
x^(2)-4x=21

To set the left-hand side of the equation equal to 0, move all the expressions to the left-hand side.
x^(2)-4x-21=0

For a polynomial of the form x^(2)+bx+c, find two factors of c (-21) that add up to b (-4).  In this problem 3*-7=-21 and 3-7=-4, so insert 3 as the right hand term of one factor and -7 as the right-hand term of the other factor.
(x+3)(x-7)=0

Set each of the factors of the left-hand side of the equation equal to 0.
x+3=0

Set each of the factors of the left-hand side of the equation equal to 0.
x-7=0

Since 3 does not contain the variable to solve for, move it to the right-hand side of the equation by subtracting 3 from both sides.
x=-3

Since -7 does not contain the variable to solve for, move it to the right-hand side of the equation by adding 7 to both sides.
x=7

The complete solution is the set of the individual solutions.
x=-3,7