Answer:
14 pounds
Explanation:
The given equations can be solved for y by substituting for x. The first equation is convenient for writing x in terms of y.
Solution
x = 20 -y . . . . . . . subtract y from the first equation
7(20 -y) +5.5y = 119 . . . . . substitute for x in the second equation
140 -1.5y = 119 . . . . . . . . simplify
21 = 1.5y . . . . . . . . . . . add 1.5y -119 to both sides
14 = y . . . . . . . . . . . .divide by 1.5
14 pounds of soy nuts should be used in the mixture.
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Additional comment
There are many ways to solve a system of two linear equations. The attachments shows a matrix solution using a suitable calculator. It tells us that x=6 and y=14, as we found above.