What is the correct descriptin for the translation of a to a? a (10, 3) - a' (1, 6)

From a to a', it is a translation transformation of T_ (-9,+3) : (x, y) - > (x-9, y+3).

The transformation a' to a is the inverse transform of the previous translation, namely

t^ (-1) : (x, y) - > (x+9, y-3)