b=a+b+c

Solution for b=a+b+c equation:

Simplifying
b = a + b + c

Add '-1b' to each side of the equation.
b + -1b = a + b + -1b + c

Combine like terms: b + -1b = 0
0 = a + b + -1b + c

Combine like terms: b + -1b = 0
0 = a + 0 + c
0 = a + c

Solving
0 = a + c

Solving for variable 'a'.

Move all terms containing a to the left, all other terms to the right.

Add '-1a' to each side of the equation.
0 + -1a = a + -1a + c
Remove the zero:
-1a = a + -1a + c

Combine like terms: a + -1a = 0
-1a = 0 + c
-1a = c

Divide each side by '-1'.
a = -1c

Simplifying
a = -1c