No, 4 is not a solution of [tex]9x - 6 = 7x[/tex].
Here's why:-
[tex]9x - 6 = 7x \\ ⇢ 9x - 7x = 6 \\ ⇢ 2x = 6 \\ ⇢ x = \frac{6}{2} \\ ⇢ x = 3[/tex]
Clearly, the value of [tex]x[/tex] is 3.
[tex]{ \bf{ \underbrace{To\:verify:}}}[/tex]
[tex]9x - 6 = 7x \\ ⇢ 9 \times 3 - 6 = 7 \times 3 \\ ⇢ 27 - 6 = 21 \\ ⇢ 21 = 21 \\ ⇢ L.H.S.=R. H. S[/tex]
Hence verified.
[tex]\large\mathfrak{{\pmb{\underline{\orange{Happy\:learning }}{\orange{!}}}}}[/tex]