Question 1007456

{{{x+4+x+x+5= 21}}}

{{{3x+9= 21}}}

{{{3x= 21-9}}}

{{{3x= 12}}}

{{{x= 12/3}}}

{{{highlight(x= 4)}}}

if {{{AB=x+4}}}, then {{{AB=4+4=8}}}