Can someone explain why b can't be written as a linear combination of v1, v2, and v3? (These are all column vectors.)

I get infinite solutions when I try to solve the equation

c1v1 + c2v2 + c3v3 = b

but they don't actually work when I plug them in.

v1 = (1, -2, 0)

v2 = (0, 1, 2)

v3 = (5, -6, 8)

b = (2, -1, 6)