I need help figuring out equations for a math problem. This is the question:

Question

For a chemistry experiment Marie needs 300 ml of a 15% acid solution.
The Science Department has quantities of 5% acid solution and 20% acid solution.
What volume of each solution is required to mix together to get her required
concentration?

I tried my best to come up with two equations needed to solve this problem and need help confirming whether or not it is correct. I don't need the problem solved just help in finding out the equations to solve the problem. If the equations I provided are not correct then if anybody could help me understand why they aren't correct and what is the correct answer and how you came to that conclusion? Thank you!

x + y = 300
0.05x + 0.2y = 0.15

Answer 1

BUT
0.05x + 0.2y = 0.15 * 300
!!!!!