The gram formula weight of phosphoric acid is 98.00 g/mol, and the density of 85.0% phosphoric acid is 1.685 g/ml. could you describe how

Formula weight of phosphoric acid is 98.00g/mol, because:
mass of H = 1g
mass of O = 16g
mass of P = 31g
mass of H3PO4 = 3*1g + 31g + 4*16g = 98g/mol

the density of 85% phosphoric acid is 1.685g/ml, so:
85% >>> we've 85g of phosphoric acid in 100g of solution (85g of acid; 100g-85g = 15g of water) 
1.685g/ml >>> we've 1.685g of phosphoric acid solution in 1ml

when we dissolve 85g of phosphoric acid in 15g of water, we obtain 85% phosphoric acid which density is 1.685g/ml