Решение:
- а) 3x + 7x + 18 = 178
\( 10x = 178 - 18 \)
\( 10x = 160 \)
\( x = \frac{160}{10} \)
\( x = 16 \) - б) 6x - 2x + 25 = 85
\( 4x = 85 - 25 \)
\( 4x = 60 \)
\( x = \frac{60}{4} \)
\( x = 15 \) - в) 7а + 5а - 14 = 130
\( 12a = 130 + 14 \)
\( 12a = 144 \)
\( a = \frac{144}{12} \)
\( a = 12 \) - г) 21а - 4а - 17 = 17
\( 17a = 17 + 17 \)
\( 17a = 34 \)
\( a = \frac{34}{17} \)
\( a = 2 \)
Ответ: а) x = 16; б) x = 15; в) a = 12; г) a = 2.