Colloid chemistry

Feb 2019
"Calculate how much surfactant is required to reach the CMC in the water phase in the presence of 100 g of oil per litre of the aqueous phase as oil droplets with radius 200 nm. The density of the oil is 0.90 gcm-3. The molar mass of the surfactant is 250gmol-1"
I have no clue how to go around answering this, so I would really appreciate some help!