[tex] = > 3x + 15 + 4x + 12 = 180 \\ = > 7x + 27 = 180 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \\ = > \: 7x = 180 - 27 = 153 \: \: \: \: \\ x = \frac{153}{7} = 21 \\ x = 21[/tex]
