Alice a net investment of S-HC.
If the price of the asset goes down, then the call options are worthless, and so the value of the portfolio at the end of the year is just that of the asset, namely Sd=$28.
By the definition of a risk-free portfolio, this value must be the same as the value of the portfolio even if the asset rises in price--a rise in price increases the value of the asset, but also increases the value of the call option Alice sold to Bob.
If the price of the asset goes up, then Bob will elect to exercise the call option, and at the end of the year Alice will have to sell H units of the asset to Bob at a price of X, receiving HX, but at the expense of having to buy H-1 units of the asset at a price Su.
Thus at the end of the year the portfolio is worth