How do I find learning curve?

Question

It took 200 labor hrs to produce 1st unit, and 60 labor hrs to produce 7th unit. Whati s the learning curve during production?

I tried doing the following, but I do not understand...

60=200x7^b

how do I solve using logs? If this is even the case...

Answer 1

60/200=7^b
log(60/200)=log(7^b)=b log(7)
so b=log(60/200)/log(7)