The correct answer would be: C. 5.02 x 10^18
Here's how you solve it!
Since the earthquake registered is 7.4 on the scale let it represent RS=7.4
The reference intensity is 2.0 x 10^11 so let it represent RI= 2.0 x 10^11
Now you need to use the formula.

Then we need to plug in the values for the formula

x
x

x

Hope this helps! :3