How to tell how many times a number has been multiplied by an other number

I am trying to multiply a number a with b until it reaches a number given c, and store into a variable how many times it has been multiplied

let’s say

a = 1000 b = 0.75 c = 500

I need to multiply the number and its result at least 3 times to get 500 or less.

I have seen about Math.log() but I am not sure that is the right method here

Any help please?