Question

How many times larger is 9 x 10^9 than 3 x 10^-4?

Answer 1

The larger value is 9 x 10^9
The smaller value is 3 x 10^(-4)

Divide the larger over the smaller
Doing so will have you divide the coefficients 9 and 3 (numbers in front of the "times ten to the..." portions) to get 9/3 = 3. 
Then you'll also subtract the exponents: 9 minus (-4) = 9 - (-4) = 9 + 4 = 13

In summary so far, we got a coefficient of 3 and an exponent of 13

So the final answer is 3 x 10^13 (assuming you want scientific notation)

If you want to convert to standard notation, instead of scientific notation, move the decimal point in 3.0 thirteen spots to the right to get 

30,000,000,000,000

there are 13 zeros (four groups of 3 plus one just after the 3) in that value above. This is the number 30 trillion