`1.`
`a)` `2/7` + `4/7` `=` `6/7`
`b)` `5/9` + `5/5` `=` `5/9` `+ 1`
`=` `5/9` + `9/9`
`=` `14/9`
`c)` `(12)/(15)` + `6/(15)` `=` `(18)/(15)`
`2.`
`a)` `5/9` `+` `5/9` `=`` .... ``+` `7/9`
`10/9` `= ... +` `7/9`
`10/9` `=` `3/9` `+` `7/9`
`3.`
`a)` `9/12` + `9/11`
`=` `3/4` `+` `9/11` `=` `(69)/(44)`
`b)` `5/10` + `21/(28)`
`=` `1/2` `+` `(21)/(28)` `=` `5/4`
`c)` `7/9` + `15/27`
`7/9` `+` `5/9` `=` `12/9`