The forward rate can be calculated using the no-arbitrage relationship between spot rates:

$(1 + S_2)^2 = (1 + S_1)(1 + f_{1,1})$

$f_{1,1} = [(1.09)^2 / 1.04] - 1 = 14.24\%$

Alternatively, we can denote this as:

$F = \frac{V_2}{V_1}$

Where $V_1$ is the value to which one dollar grows by time $T_1$ and $V_2$ is the value to which one dollar grows by time $T_2$.

In this case,

$F = \frac{V_2}{V_1} = \frac{1.09^2}{1.04} = 1.1424$

So that $F = 1.1424 - 1 = 14.24\%$