Question 971230
*[invoke substitution "x^2-2x", "x", 3 ]10x+y=840 
6x+2y=1036

y=-10x +840

Substitute
6x + 2(-10x +840)=1036

distribute
6x-20x+1680=1036

-14x = -644
x= 46

10x+y=840
460+ y=840
y= 380

Other equation

46*6 + 2(380) should equal 1036

276 + 760 =1036

x=46
y=380