What is the solution of the square root of 3x+28-8=x (-8=x is not in the square root) any explanation and answer is appreciated!

When you use a graphing calculator to solve these, it is generally convenient to rewrite the equation so you are looking for a zero.
.. √(3x +28) -8 -x = 0

x = -4 . . . . . . from the graph

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If you add 8 and square both sides, you get
.. 3x +28 = (x +8)^2
.. x^2 +13x +36 = 0
.. (x +9)(x +4) = 0
.. x = -9 or -4 . . . . . . . the -9 solution is extraneous