The above stress is approximated by a sinusoidal function (i. e. sine wave) with a mean 3,526 kPa and amplitude 260 kPa at a frequency of 6 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 3 times the frequency of the first component and half of the magnitudes of the first component. The format for the Fourier series for the stress signal for this flight condition is given below: y(t)2 = { z1 + z2 * sin (d2*π t) + z3 * cos (d3*π tπt) } kPa. Where the second term corresponds to a lower frequency compared to the third term. Provide the value of z1 (using 2 decimal places).