Answer :
[tex]23x+70=x^2-70\\
x^2-23x-140=0\\
x^2+5x-28x-140=0\\
x(x+5)-28(x+5)=0\\
(x-28)(x+5)=0\\
x=28 \vee x=-5[/tex]
x can't be negative so [tex]x=28[/tex]
x can't be negative so [tex]x=28[/tex]