\[\boxed{\text{327\ (327).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[1)\ \overline{\text{cab}} + \overline{\text{ca}} =\]
\[= 100c + 10a + b + 10c + a =\]
\[= 110c + 11a + b.\]
\[2)\ \overline{\text{abc}} + \overline{\text{bca}} =\]
\[= 101a + 110b + 11c.\]
\[3)\ \overline{ab9} + \overline{7a} =\]
\[= 100a + 10b + 9 + 70 + a =\]
\[= 101a + 10b + 79.\ \]