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.
Answer:
19.488
Step-by-step explanation:
8.12 x 2.4 = 19.488
2/3 - 1/5
make a common denominator
10/15 - 3/15
simplify
7/15 is your answer
hope this helps