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?