Question 1071931
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You math model is this system of two linear equations in two unknowns

  x +   y =   80,     (1)
90x + 80y = 6930.     (2)


Can you solve it ?

Do you know how to solve it ?


HINT: express x = 80 - y from (1) and then substitute it into (2) replacing x.


You will obtain a single equation for y, which you can easily solve.


This is "the Substitution method".
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