[tex]10 n-3 = 7n+21[/tex]
Add 3 to both sides :
[tex]10n-3+3=7n+21+3[/tex]
[tex]10n=7n+24[/tex]
Subtract 7 n from both sides:
[tex]10n-7n=7n+24-7n[/tex]
[tex]3n=24[/tex]
Divide both sides by 3 :
[tex] \frac{3n}{3} = \frac{24}{3} [/tex]
[tex]n = 8[/tex]
hope this helps!