Can anyone help me with this problem?

Question

A pharmacist mixed 10% saline solution with 15% saline solution to get 100mL of 12% saline solution. How much of 10% saline solution did the pharmacist use in the mixture?

Answer 1

Let x = the amount of the 10% saline solution, then

100-x = the amount of the 15% saline solution.

.10(x) + .15(100-x) = .12(100)

Solve for x.