let us the substitution x=y^2. So we get
[tex]\begin{gathered} y^2-3y-28=0 \\ (y-7)(y+4)=0\rightarrow \\ y=7,y=-4 \end{gathered}[/tex]having this we get that the answer are:
[tex]x=49[/tex]The option y=-4, can not be used because we get that
[tex]\sqrt[]{x}=-4[/tex]and it is not possible
