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

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?

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$2h = n^2 \cdot 10^{-6} s$. Now $1h = 60\cdot 60s$... –  Vittorio Patriarca Jun 5 '12 at 14:40

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

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

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Thank you both for the insight. I understand the problem now. Much appreciated. –  Jack S. Jun 5 '12 at 14:58