6) We apply the square root to both sides to undo the squaring operation.
7) The photo without the frame is 8 by 10 since we add on two copies of x to jump from 8 to 8+2x. Similarly, we go from 10 to 10+2x.
8) The x represents the thickness of the frame. The 100 is the total area (picture + frame). The expression on the right hand side is also the total area.
9) Apply the zero product property to set each factor equal to zero. You'll find that x+5 = 0 leads to x = -5. Also, 2x-3 = 0 becomes 2x = 3 and solves ultimately to x = 3/2
