Question 428471
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Pay close attention to the solution from tutor @ikleyn.<br>
In a typical algebra class, given a system of two linear equations, you are taught to solve one of the equations for one of the variables (by itself) and substitute the result in the other equation.<br>
But as the tutor shows in this problem, the solution is much easier because the expression "15x" appears in both of the given equations; so solving one of the equations for "15x" and substituting in the other equation makes the solution easy.<br>