If i got internet speed 20MB/s so the monthly is like 20 * 60 * 60 * 24 * 31 = 53 568 000 Am i wrong?
You can use Google to do this type of math for you:
20Mbps x 1 month
Google says: 6.26979788 terabytes
or 20Mbps x 7 days
Google says: 1.44195557 terabytes
Google has some neat features like this.
You can also use it to convert: 1.44195557 terabytes to MB
gives you: 1 512 000 megabytes
Is your speed 20MB/s or 20Mbps? 20 MegaBytes is quite a bit more than 20 Megabits. You'd need to add the 8bits/byte in there to convert from bits in network speeds to data volume if that is the more usual 20Mbps. And you're likely to want to take that down to GB or TB, also
The best way to draw this out is to cancel units as you go. In each step you can cross out a top unit like "min" with one from the step previous on the bottom. Helps to show your work:
At continuous peak loads a 20Mbps circuit could push over 6TB. But you should expect to barely be able to run at 80% and factor in some loss for protocol overhead based on what form of data transfer you're doing. I usually fudge factor to 2/3rds of theoretical max. IF you try HARD I bet you can average 4TB a month on that circuit.