Max size of the problem that can be solved in 2 hours if the algorithm takes n^2 microseconds

Question

I have been going through my textbook trying to solve this problem but I can't seem to completely understand. It seems so simple yet I can't figure it out. How do I go about solving this?

Answer 1

2 hours is equal to $2\times 3600\times 1000000$ microseconds which is $7200000000$ microseconds.

So you want to find $n$ such that $n^2 = 7200000000$.