√84 is your irrational number
a rational number is a number that can has an ending (terminated number)
so √9 = 3
1.9 = 1.9 (it does not continue, or unless it has a line over x amount of numbers
√81 = 9
So it leaves √84, which = 9.16515138991.....
so √84 is your answer
hope this helps
