The answer is CH₃O₆
An empirical formula is the simplest ratio. So, let's simplify the ratio
14 : 42 : 84
All numbers are divisible by 14, therefore:
14 : 42 : 84 = (14/14) : (42/14) : (84:14) = 1 : 3 : 6
So, it contains 1 C-atom, 3 H-atoms, and 6 O-atoms