You have already gotten some direct answers, but here are a few other things to think about.
You didn't state it explicitly, but you implied you want 30mA thru the LED. Is this really correct? Certainly there are LEDs and applications for which this is valid. This is not meant as a offence, but if you're here asking a basic Ohm's law question you probably have a common T1 or T1-3/4 LED which is most likely rated for 20mA.
Despite what the maximum allowed current is, you need to consider what the purpose of the LED is. Is it for illumination? In that case you probably do want the maximum light you can get. However, your picture implies it's a red LED, so I'm guessing not. If this is just a indicator, you don't need to run it anywhere near its maximum current unless there are unusual circumstances like it needs to be visible in sunlight. Full current can make the result uncomfortably bright as a indicator for a indoor device. I usually run 5mA thru a 20mA LED for indicator use.
Is the power coming from a battery? If so, it is likely worth getting a more efficient LED and running it at a lower current.
My second comment is about your equation, "3/0.03 = 100 Ohm". Please be more careful with units. That will not only communicate your intentions better, but make it more likely you think about the underlying physics better. Technically your equation is incorrect since the ratio of two dimensionless numbers can't result in a value in Ohms. From context, you meant 3 Volts divided by 0.03 Amps = 100 Ohms.
While that would at least make it correct, I recommend to write values in electronics in engineering notation. That means use a power of 1000 such that the value is at least 1 but less than 1000, then apply the appropriate prefix. In this case, 0.03 Amps is better said as 30 milliAmps, or 30 mA. I know this can seem arbitrary and inconvenient to beginners, but it's worth learning and getting used to. After a while you'll form a picture in your mind what a milliamp, microvolt, kiloOhm, etc, is. Those skilled in the art whom you hope will answer your question likely had to look at 0.03 Amps and then think to themselves "Ah, he means 30 mA".