`a)` 

`2x - y =4`

` <=> y = 2x - 4`

` <=> {(x \in RR),(y = 2x - 4):}`

`b)`

`x + 3y = -3`

` <=> x = -3 - 3y`

` <=> {(y \in RR),(x = -3 - 3y):}`

`c)`

` 0x - 2y = 4`

` <=> -2y = 4`

` <=> y = -2`

` <=> {(x \in RR),(y = -2):}`

`d)`

`3x + 0y = -6`

`  <=> 3x = -6`

` <=> x = -2`

` <=> {(y \in RR),(x = -2):}`

`e)`

`2x + 3y = 0`

` <=> 3y = -2x`

` <=> y = 1/3 * -2x `

` <=> y = -2/3 x`

` <=> {(x \in RR),(y = -2/3 x):}`

`f)`

`4x = 5`

` <=> 4x + 0y = 5`

 ` <=> x = 5/4`

` <=> {(y \in RR),(x = 5/4):}`