How do you convert 30 ml into grams?

Well it depends on the type of concentration you're looking for, molar or mass. In the first case you need to calculate how many moles of matter you have using it's molar mass which you can find in the Periodic Table the formula is number of moles= mass/molar mass, then you convert 200 ml in liters ie 0.2 and divide that by the number of moles you found previously.

If you are just searching for the mass concentration, simply divide 200 by 30, be careful though since you will have grams per milliliters in the end, you can convert 200ml to 0.2L and then divide if you want grams per liters.

Hoped this helped!