I don't understand what I am doing wrong. Please help me to solve d and e.

transaction deposit after portfolio switch = 750+10=$760 billion.

reserve requirement = 0.05*760=$38 billion.

hence , total lending capacity = 760-38=$722 billion.

total lending capacity of the banking system after the portfolio switch will be $722 billion.

e.

if the banks fully utilize their lending capacity

total transaction deposits with bank =$760 billion.

cash reserve ratio=0.05

total reserve = 0.05*760 = 38

money leant by banks in the economy = 760-38=$ 722 billion

cash held by public = 450-10=$440 billion

total money supply = $722+440= $ 1162 billion