There something you ain’t giving us in this equation
The number X is placed somewhere between 9 and 10. That's because 9 squared is 81 and 10 squared is 100.
Here, regrouping is basically carrying.
64+43 shown vertically would be:
64
+43
-------
107
4+3 is 7, so seven is in the ones place, but that's not the point.
60+40 is 100, so you regroup by carrying the one to the hundreds place.
Hope I helped!
