Can you explain step by step for #15 and #16 i have a test on this tomorrow

15.

16. 10 ml of 20% saline and 40 ml of 10% saline

Step-by-step explanation:

A chemist takes x ml of 20% saline and y ml of 10% saline. In total, he takes

x + y ml that is 50 ml, so

There are   ml of salt in x ml of 20% saline and ml of salt in 10% saline. There are ml of salt in 50 ml of 12% saline. Thus,

15. We get the system of two equations:

16. Solve this system. From the first equation:

Substitute it into the second equation: