A piece of green jade has a mass of 26.123g. If the sample of jade displaces 50.

This is basically the same thing, just different units. The formula for density is still D=M/V. You're given the mass, so you need the volume. Your initial speculation was correct, you do subtract 57.5 - 50.0 mL. This is an irregular object problem, it's Archimedes in his bathtub (The legend goes he was asked to find out if gold was pure, and when he got in his bathtub he displaced the water and realized that he was an irregular object so you could figure out the volume of irregular objects by displacing water. In reality it's pretty inaccurate, but it works-ish.). So the volume is 7.5mL. 26.123g/7.5mL = 3.48 g/mL( rounded). You can leave it like that because they didn't ask for it in different units, but as an aside the typical unit for density of this sort is kg/m^3. I can't do that in my head, so I looked up a converter and it's: 3480 kg/m^3. If you haven't been taught to convert that yet, don't worry about doing it and just leave the problem in the units you're given.

This is how you work it out :
The piece of jade displaced 7.5 mL (7.5 cm^3) of water (57.5 - 50.0 = 7.5)
26.123 g / 7.5 cm^3 = 3.48 g/cm^3

Im still trying to figure this one out

3.48 g/cm

Yes.  I remember this from my class