the solution of dextrose has a w/v% of 70 %. this means the mass of dextrose is 70 % of the volume of the solution.
In 100 mL of the solution - mass of dextrose is 70 g
therefore in 400 mL of the solution - mass of dextrose is - 70 /100 x 400 = 280 g
mass of dextrose is 280 g