Do you know how I could figure this out?

Let Lo represent the loudness of a sound at 0dB, the threshold of hearing.

a) write an equation to express the loudness , L, of a sound with decibel level, d.

I know that this answer is Lo= Lo(10) d/10

b) How many times as loud as a heavy truck is an air conditioner?

the heavy truck is 90 dB and an air conditioner is 65.