Apply angle sum property
[tex]\\ \tt\Rrightarrow 4x-12+63+45=180[/tex]
[tex]\\ \tt\Rrightarrow 4x+51+45=180[/tex]
[tex]\\ \tt\Rrightarrow 4x+96=180[/tex]
[tex]\\ \tt\Rrightarrow 4x=84[/tex]
[tex]\\ \tt\Rrightarrow x=21[/tex]
Answer:
x = 21°
Explanation:
All the interior angles of the triangle sum up to 180°
45 + 63 + 4x -12 = 180°
96° + 4x = 180°
4x = 180° - 96°
4x = 84°
