The number of cows is given by
So, after years, the number of cows will be
We want this number to be twice as much as the original:
First of all, we can cancel 14 from both sides:
Finally, on the right hand side, we can use the exponent rule
to get
To solve this equation, we must impose that the two exponents are the same:
And clearly this is true if and only if . So, it will take 5 years for the cow heard to double in number.
You can do the exact same steps to find the doubling time for the sheeps.