Let (Z ≠ Z, ⊕) be the abelian group where (a, b) ⊕ (c, d) = (a + c, b + d) - here a + c and b + d are computed using ordinary addition in Z - and let (G, +) be an additive group. If f (1, 3) = g1 group homomorphism where f(1, 3) = g1 and f(3, 7) = g2, express f(4, 6) in terms of g1 and g2.