First, we have to find the moles of Li3PO4 to answer this question. From the mass of lithium, we can use it to find the total mass of Li3PO4 by using percentages. Then this mass will now be used to find the moles of Li3PO4 using also its molar mass.
The molar mass of Li3PO4 is 115.79 g/mol. If lithium is 6.9 g/mol, multiplied by 3, that would be 20.7 g/mol. Now we can use this to find the percentage of Li in Li3PO4, 20.7/115.79 = 0.1788 or 17.88%
This 17.88% can tell us the mass of Li3PO4 using the mass which 0.284. Now lets divide 0.284 by 0.1788 = 1.589 g. This now the mass of Li3PO4.
Using that, we can now easily find the moles of Li3PO4, using again the MM. So (1.589g)(1mol/115.79g)=0.013723 moles of Li3PO4.
From this, we can now find the volume using molarity (0.362), which is moles per Liter. (0.013723 moles)(1L/0.362mol)=0.03791 L
Hope that makes sense!