$\text{Cho a,b € Z. Tìm x€ Z sao cho :}$
$\text{a, x – a = 2}$
`->` $\text{x = 2 + a}$
$\text{b, x + b = 4}$
`->` $\text{x = 4 - b}$
$\text{c, a – x = 21}$
`->` $\text{x = a - 21}$
$\text{d, 14 – x = b + 9}$
`->` $\text{x = 14 - ( b + 9 )}$
`->` $\text{x = 14 - b - 9}$
`->` $\text{x = 5 - b}$