This homework is due soon and i can't get this one problem... it's driving me crazy.

Here it is: Prove and extend or disprove and salvage (with another if and only if statement):

Statement: Let m and n be two relatively prime integers each greater than 1. Then for integers a and b, the system of simultaneous linear congruences

ax=b mod m

ax=b mod n

(the "=" is supposed to be three lines instead of two, meaning "congruent to")

has a solution of integer x if and only if there is an integer solution to the linear congruence

ax=b mod mn

(again, three lines on the "=")

You don't have to write out a formal proof for me, just help me understand this and lead me in the right direction so i can write a proof for it. Thanks!