We are given
[tex]\sqrt[\square]{x+3}\text{ = 12}[/tex]Square both sides of the equation
[tex]\begin{gathered} (\sqrt[\square]{x+3})^2=12^2 \\ x+3\text{ = 144} \end{gathered}[/tex]subtract 3 from both sides
[tex]\begin{gathered} x+3-3\text{ = 144-3} \\ x\text{ = 141} \end{gathered}[/tex]Hence the value of x is 141
