The above stress is approximated by a sinusoidal function $($i$.$e$.$ sine wave$)$ with a mean $3,316$kPa and amplitude $298$ kPa at a frequency of $7$ Hz $.$ At a second flight condition, the stress had an additional sinusoidal component $($i$.$e$.,$ in addition to the first sinusoidal function above$)$ that has $4$ times the above frequency, half of the magnitudes, and was $90$ degrees out of phase $($leading$).$The format for the fourier series for the stress signal for this flight condition is given below:

$y(t{)}_2=\{z1+z{2}^{**}sin(f{2}^{**}2t)+z{3}^{**}$ trigfunction $(f{3}^{**}2t)\}kPa.$

Where the second term corresponds to a lower frequency compared to the third term.

Provide the value of f $3($using $2$ decimal places$).$