Solving a percent mixture problem using a system of linear equations

Question

A scientist has two solutions, which she has labeled Solution A and Solution B. Each contains salt. She knows that Solution A is 70% salt and Solution B is 95% salt. She wants to obtain 50 ounces of a mixture that is 80%  salt. How many ounces of each solution should she use?

Answer 1

.95B + .7[50-B] = .8[50]

.95B-.7B = .8[50]-.7[50]

.25B =5

B = 20

A =50-20 = 30

.95-.8= .15

.8-.7 = .1

.1/.15 = 2/3 = 20/30