Question 62114
1st: x+y=10
2nd:  y=x-4 
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Substitute the value for y into the 1st equation, as follows:
x+(x-4)=10
Simplify to get:
2x-4=10
2x=14
x=7
Now, substitute that value of x into the 2nd equation to solve for y, as follows:
y=7-4=3
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Now check those answers in the 1st equation as follows:
7+3=10
10=10
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Solution:
x=7 and y=3 is the solution for the system of equations.
Cheers,
Stan H.