Step-by-step explanation:
[tex](25x) + (57 + x) = (45x) (ext. \: angles \: of \: a \: triangle) \\ 25x + x- 45x = - 57 \\ \frac{ - 19x}{ - 19} = \frac{ - 57}{ - 19} \\ x = 3[/tex]
Goodluck
