Question

(x+12)•13-(x+12)•9=80

Answer 1

(13x+156)-(9x+108)=80
4x+48=80
4x=80-48
4x=32
x=32:4
x=8

Answer 2

$(x+12)*13-(x+12)*9=80$
$(13x+156)-(9x+108)=80$
$13x-9x+156-108=80$
$4x+48=80$
$4x=80-48$
$4x=32$
$x=32:4$
$\boxed{x=8}$