If $m$ and $n$ are relatively prime, then for every $a,b$ there exists $x$ such that $x\equiv a \pmod m$ and $x\equiv b \pmod n$

Question

Possible Duplicate:
Prove the Chinese Remainder Theorem

Suppose $gcd(m, n) = 1$. Show that for every pair of integers $a, b$, there exists an integer $x$ such that

$x \equiv a \pmod m$ and $x \equiv b \pmod n$

By $gcd$ I mean greatest common divisor.