Please Simplify 8(x+2)-4x+7

8(x+2)-4x+7 = 0
8x+16-4x+7 = 0
4x+23 = 0
x = -23/4

8(x+2)-4x+7=8x+16-4x+7
                    =4x+23
x=-23/4.

Please simplify x^2+8x+7

I am taking it from your statement.

8x+16-4x+7=0
4x+23=0
4x=-23
x=-23/4

Simply by factorisation

X^2+7x+x+7= x(x+7)+1(x+7)= (x+1)(x+7)

putting this equal to zero we get solution for x as -1  or -7 ( if you are asked to solve it further asa quadratic equation)