For this question we will be using two main formulas:
1. Finding the number of moles of the compound, since we have mass and the molar mass of NaC2H3O2 is 82.03g/mol
Molar mass = mass/number of moles
We already have molar mass and mass
82.03 = 12.2g/number of moles
n = 12.2/82.03
n = 0.15 moles of NaC2H3O2
2. Now we can find the volume in mL, by using the Molarity formula, which is:
Molarity (or concentration) = number of moles/volume in Liters
We already have the molarity and number of moles
0.210 M = 0.15 moles/V in L
V = 0.15/0.210
V = 0.714 L or 714 mL