Verified answer

(1-2i)z = 6 - 3i - (3 + 3i)

(1-2i)z = 3 - 6i

z = (3 - 6i) / (1-2i)

z = [(3 - 6i) * (1+2i)] / [(1-2i) * (1+2i)]

z = [(3 - 6i)(1+2i)] / (1 - (2i)²)

z = [(3 - 6i)(1+2i)] / (1 - (-4))

z = [(3 - 6i)(1+2i)] / 5

z = [(3 + 6i - 6i - 12i²)] / 5

z = [(3 + 6i - 6i + 12)] / 5

z = 15 / 5

z = 3