I will assume that the glucose solution is being added to
Your initial solution had a concentration of
Now, you don't have to calculate the amount of solute present in the initial solution, all you have to do here is figure out what the total volume of the solution will be after the dilution.
#V_"total" = "25 mL" + "375 mL" = "400 mL"#
You can say that the initial solution is being diluted by a factor of
#"DF" = (400 color(red)(cancel(color(black)("mL"))))/(25color(red)(cancel(color(black)("mL")))) = color(blue)(16) ->#this is the dilution factor
This means that the diluted solution contains
Therefore, you can say that the concentration of the diluted solution is
#"% diluted" = "15%"/color(blue)(16) = color(darkgreen)(ul(color(black)(0.94%)))#
The answer is rounded to two sig figs.