Hey there!
mass of solvent :
volume in mL => 2.74 * 1000 => 2740 mL
D = m / V
0.997 = m / 2740
m = 0.997 * 2740
m = 2731.78 g of solvent
Therefore :
T % = ( mass solute / mass solute + mass solvent ) * 100
T% = ( 199 / 199 + 2731.78 ) * 100
T% = ( 199 / 2930.78 ) * 100
T% = 0.0679 * 100
T = 6.79 % of NaCl
hope this helps!