calculus – Proof of derivatives of exponential function

I am learning Calculus and I ran into the proof regarding the exponential derivative, I haven’t quite understood it though, could you guys please help me out with that? The proof goes like that:

y = a^x
ln(y) = ln(a^x)

Here comes the part I haven’t gotten yet, why is y’/y = lna?

y´/y = lna
y´= lna(y)
y´= lna(a)(a^x)

Thanks in advance!