Transfer price

Bath co question

part a) total group profit 10160

Part b) total group profit 11060

Variable cost of making fittings-20$
Variable cost of buying fittings–65$
extra variable cost of buying====45$

Variable cost of making fittings—20$
external market price—————–80$
========================60

extra cost if division A buys from division divison B 60-45=15$

dedcut b -a=900(15*60000 if it buys the reamining from outside supplier)

dear tutor is this the right approach for part b?