The first thing you need to do is convert mL into L
so (175 mL)(.001L/1mL)=.175L then you multiply by the Molarity of H3PO4 which is 3.5mol/L so (.175L)(3.5mol/L)=.6125 mol H3PO4, and since it wants the answer in grams you then multiply (.6125molH3PO4) by the molar mass of H3P04 which is about 97.99g and your answer is 60.02g which is about 60 grams of H3PO4. Hope this helped