Answer is: 71.43 milliliters of the stock solution are needed.
V(solution of glucose) = 500 mL; voume of the solution.
ω(solution) = 5.0% ÷ 100%.
ω(solution) = 0.05.
ω(stock solution) = 35% ÷ 100%.
ω(stock solution) = 0.35.
Because weight of the glucose is the same in both solutions:
0.05 · 500 mL = 0.35 · V(stock solution).
V(stock solution) = 500 mL · 0.05 ÷ 0.35.
V(stock solution) = 71.43 mL.