if 30 mL of a 0.5 % solution is being prepared from a 6% solution, ___ mL of the 6% solution will be used?

0.5% of a 30 mL solution would be 0.15 mL of ingredient. Then we have to find the quantity of 6% solution that has 0.15 mL of ingredient.

(qty of 6% solution)(6%) = 0.15 mL
divide both sides by 6%:
qty of 6% solution = 0.15 / 0.06 = 2.5 mL

After taking 2.5 mL of the 6% solution, you fill in the rest with an inert solvent (I'm guessing water, since I haven't seen this problem on Khan Academy).

Thank you Steven I really appreciate your help!