Find $a+b+c$, given that $x+y\neq -1$ and $$\begin{align*} ax+by+c&=x+7,\\ a+bx+cy&=2x+6y,\\ ay+b+cx&=4x+y. \end{align*}$$

Find  $a+b+c$ , given that  $x+y\neq -1$  and  $\begin{align*} ax+by+c&=x+7,\\ a+bx+cy&=2x+6y,\\ ay+b+cx&=4x+y. \end{align*}$

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(ax + by + c) + (a + bx + cy) + (ay + b + cx)  =  (ax + by + c) + (a + bx + cy) + (ay + b + cx)

(ax + by + c) + (a + bx + cy) + (ay + b + cx)  =  (x + 7) + (2x + 6y) + (4x + y)

ax + by + c + a + bx + cy + ay + b + cx  =  x + 7 + 2x + 6y + 4x + y

ax + bx + cx + ay + by + cy + a + b + c  =  7x + 7y + 7

x(a + b + c) + y(a + b + c) + 1(a + b + c)  =  7(x + y + 1)

(a + b + c)(x + y + 1)  =  7( x + y + 1)

a + b + c  =  7