Question 1206950
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I agree with the other tutor on the steps and final answer she wrote out. There's not much for me to add other than to think of "substitution" as in a "substitute teacher".


The substitute teacher is a temporary replacement for your original teacher until she or he gets back. 
In this case, 5x-13 substitutes in for y, since both are equivalent.
That's how we go from 5x+2y = 19 to 5x+2(5x-13) = 19


It might help to color code things like so
5x+2y = 19
5x+2( <font color=red>y</font> ) = 19
5x+2( <font color=red>5x-13</font> ) = 19
which may illustrate the substitution process a bit better.
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