Answer:
b) 4x
Step-by-step explanation:

A
rational number is any number that can be written as the
ratio between two other numbers i.e. in the form

Part A:
An easy choice that makes sense is 7.8, right in the middle. To prove that it's rational we need to write it as a ratio. In this case we have

Part B:
We need a number that can't be written as a ratio (because it neither terminates nor repeats). Some common ones are

,

,

and

so it makes sense to try and use those to build our number. In this case

works nicely.
It would be sixty six hundred thousand four hundred and seventy-two.
If I am reading the question correctly it would come out to -6x+42 First do all the addition and squaring, then factor in that negative. You come out to -2x^3 +2x^3-4x-2x+25+5+9+3. The x^3's cancel, the -x's add to -6x, then all that other adds to 42.
A graphing calculator working the quadratic regression problem for these three points gives the equation as
y = 2x² +7x -5