How to find Log10(x) without Math library

Question

I have the following code. I need to calculate log10(x) without math function. How can i do this?

class Solution(object):
    def findPower(self, number, exponent):
        resultPower = 1
        for i in range(1, int(exponent) + 1):
            resultPower = resultPower * number
        return resultPower

    def log10(self,x):
       ...

    def mySqrt(self, x):
        return self.findPower(10, (self.log10(x)) / 2)

I've found the formulas.

But how i should use it ?