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x in (-oo:+oo)
(1/5)*(x+15)+(1/8)*(x+8) = x+6 // - x+6
(1/5)*(x+15)+(1/8)*(x+8)-x-6 = 0
1/5*(x+15)+1/8*(x+8)-x-6 = 0
1/5*(x+15)+1/8*(x+8)-x-6 = 0
13/40*x-x-6+4 = 0
4-27/40*x-6 = 0
-27/40*x-2 = 0
-27/40*x-2 = 0
-27/40*x-2 = 0 // + 2
-27/40*x = 2 // : -27/40
x = 2/(-27/40)
x = -80/27
x = -80/27
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