Given data:
The first nummber is a=5.1x10^12.
The second number is b=6.3x10^9
The second number can be written as,
b=0.0063x10^12
As, the first number have 10^12 as the exponent and second number also have the same exponent.
we know very well
5.1>>0.0063
Thus, the first nummber is greater than second one.