Answer :

luana
[tex]x-(4x-7)=5x-(x+21)\ \ \ \ | omit\ the\ brackets\\\\ x-4x+7=5x-x-21\\\\ -3x+7=4x-21\ \ \ | subtract\ 4x\\\\ -7x+7=-21\ \ \ | subtract\ 7\\\\ -7x=-28\ \ \ | divide\ by\ -7\\\\ x=4[/tex]