Passive Filters - Engineering

Q1:

At a certain frequency, the output voltage of a filter is 6 V and the input is 12 V. The voltage ratio in decibels is

A 6.02 dB

B –6.02 dB

C 12.04 dB

D –12.04 dB

ANS:B - –6.02 dB

How to calculate decibel values without calci?

Can anyone suggest me.