Finding the function of a set of numbers

Okay, let me preface this as this is my first post and this is not for assistance in a math class rather a question in analytics. I have a few sets of numbers and I'm trying to figure out the function of how x & y interact to give me say z. I know for at least half of my problem my good 'ole Ti-84 can solve it, its just been so long since I've used it that I can't remember how to do it. The latter problem has more variables so I'm not sure that the Ti-84 can help.

Part 1 - the ceiling.

X-----Y

_______

75----51

76----51

77----52

78----53

80----54

etc....

^The above I believe I can plug into the calculator and it will spit me out a formula for a "Best fit" which may or may not work, but it will be a step in the right direction.

Part 2 - Where to begin

Below the first two numbers interact in such a way that they equal the third number, AND at the same time the second set of numbers interact to give the sixth number. Any ideas how I would go about finding the equation that is true for these figures?

107300 212000 =17 U 267500 117700 =79

111800 212000 =19 U 267500 121750 =73

114020 212000 =22 U 267500 124110 =70

137702 212000 =29 U 267500 =67