40.sagews

a,b,c = var ('a,b,c')

q3 = 2 == b + a
q2 = (-10 + 2*a + 2*(a - c) + 2*(a - c) == 0)
q1 = (2*(c - a) + 2*(c - a) - 6 == 0)
show(solve ((q3,q1,q2), a,b,c)[0])

\left[a = 8, b = -6, c = \frac{19}{2}\right]