Explanation

The GRE calculator will not be able to handle that many zeros. Start this calculation on paper. To make things easier, you could cancel as many zeros as you want, as long as you do the same operation to both quantities. For instance, you could divide both sides by 1,000,000,000,000 (just think of this as “1 with 12 zeros”), to get:

Quantity A	Quantity B
$30 \times 2$	$15 \times 4$

Or, just use a bit of logic: 30 million times 2 million is 60 million million, and 15 million times 4 million is also 60 million million. (A “million million” is a trillion, but this doesn’t matter as long as you’re sure that each Quantity will have the same number of zeros.)

Hence option C is correct!