Here is the problem:
A dietitian has 3 supplement products that can be used.
Each dose of Supplement I contains 5 units of Vitamin B, 4 units of calcium and 4 units of iron.
Each dose of Supplement II contains 2 units of Vitamin B, 3 units of calcium and 2 units of iron.
Each dose of Supplement III contains 1 unit of vitamin B, 5 units of calcium and 2 units of iron.
If the patient needs 13 units of Vitamin B, 16 units of calcium and 12 units of iron each week, how many doses of each supplement should the dietitian prescribe?
Then: I have $x=1+z,\quad y=4-3z,\quad$ and $(1+z,4-3z,z)$
Now I'm confused on how to interpret this into doses, if this is the right approach. Please help.