I agree with you here.

The investor has both (1) sold a call option and (2) bought a put option.

The investor has effectively insured herself against any volatility in the stock price.

If the stock price is less than $80 then she exercises the put option and sells the stock at $80. If the stock price is more than $80 then whoever she sold the call option to will want to buy it at $80. So again she sells it at $80.

In either case the investor sells the stock at $80 and she pays the bank $78.54. There is a risk free gain of $80-$78.54= $1.46.

I get the same answer for both C3 and C4 ($1.46)