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physics.nist.gov/cuu/Units/prefixes.html
You just have to memorize this stuff, at least the ones you work with all the time. It's ok to bookmark the page so you can look up the others when you run across them.
There is a prefix every three powers of ten, except for 100, 10, 1/10, and 1/100. To go from one to another you use the LARD rule: LEFT ADD RIGHT DEDUCT. When moving the decimal to the LEFT you ADD to the power of ten. When going to the RIGHT you DEDUCT from the power of ten.
A conversion factor is a fraction equal to 1. You are given that one hour equals 60 minutes so you can write that as hr/60min=1 or 60min/hr=1 whichever works for you and drop it into an equation anywhere and it only changes the units.
ANSWER = You write this first so it looks like you know what you are doing. That gives you a bit of time to figure out what to do next.
ANSWER = 2.3L x 1/200mL x 1000mL/L
Ok, now we check everything. This is called sanity check and it is especially important in chemistry and physics where you might have a dozen or so conversions in a single equation. We have L above the fraction line and again below so that cancels. We have mL above and below so that cancels. The answer is a number just like we want.
When you are sure everything is right, multiply all the numbers above the line and divide by all the numbers below the line.
ANSWER = 2.3L x 1/200mL x 1000mL/L = 11.5