Thank you guys for your help, I have a much more clear understanding of the problem. However, one more thing, with the calculations from the paper, it is possible to find the probability the attacker would catch up ever, at any point in time later. But what if we limit the time the attacker has to catch up? Let's say the block generation time is 10 min per block as already mentioned and we give it 1h of time, so 6 blocks to overtake the honest chain while starting 1 block behind. The probability of overtaking under this condition is what I'm trying to figure out how to calculate. Really thank you for the help.

Dear all, I have a technical question about Bitcoin which is kind of like a homework assignment that I do not completely understand. I apologize if this is the wrong place for such a discussion, but I hope there is going to be some enthusiast willing to look into this. So here it goes (the question):
Let us assume that the Bitcoin network’s mining power is 100 hash/s. For this task let us assume the difficulty does not change. Find the confirmation and payout time of
a chosen Cryptocurrency exchange for BTC. Calculate how much hashing power does an attacker need to control in order to create a valid sidechain that would overtake the
main chain from 1 block before the height of the transaction sent to the exchange in:
1 hour / 1 day / 1 week
We always count with a block generation rate that averages 10 minutes from what I understand? What does the attacker need to achieve in order for his sidechain to overtake the main chain, all I understand is that he would need to have at least the hash power of the network, which is 100 hash/s here, but that seems too simple. Also i do not really understand the following part of the sentence from 1 block before the height of the transaction sent to the exchange.
Thank you for any kind of suggestion.