Answer:
0.0185 or 1.85%
Explanation:
The payoff table shows that the portfolio is riskless with time-T value equal to $55.
Position
ST < 55
ST > 55
Buy stock: ST, ST
Short call: 0, -(ST - 55)
Long put: (55 - ST), 0
Total: 55, 55
The risk-free rate is: ($55/$54) - 1 =0.0185
=1.85%
Therefore the payoff of the portfolio is $1.85%