What is x if rs= 6, st=9, tu=7, uv=15,vr=14

When I leave home to walk to school2And what I think I've seen3Now, what can I say4And I've kept careful track5Just a broken down wagon6When Isay that i saw it on Mulberry St7The story would really be better to hear8A reindeer is better; he's fast and he's fleet9To pull a thing that runs on wheels10Jack or Fred of Joe or NAT-11Say! That makes a story that no one can beat12But he'd look simply grand13If a man sits and listens while hitched on behind14But now what worries me is this...15To guide them through where's traffic's thick-16And he raises his hat as they dash by the stand.17With a roar of its motor an airplane appears18A big magician doing tricks..19For I had a story that NO ONE could beat!20There was so much to tell, I JUST COULDN'T BEGIN!21"Nothing," I said, growing red as a beet