Panjang TR = ??? Kelas 9 Matematika Bab Kesebangunan

panjang TR = x
 12 + x/9+11 = 9/12
12+x/20 = 9/12
12 (12+x) = 9 x 20
144+12x = 180
12x = 180 - 144
12 x = 36
x = 36 : 12
x = 3

maaf kalau salah.