Can someone help me out with this sinusoid question My answe

Can someone help me out with this sinusoid question? My answer was -24*pi radians but its wrong

A signal, s(t) = cos (Ohm_0 t), where Ohm_0 = 2 pi F_0 = 2 pi * 8 is the frequency in radians/second, is delayed (shifted to the right) by 1.5 seconds to give s_d = s(t - 1.5). Calculate the principal value of the phase shift of the resulting signal, S_d(t). Recall that cos (theta) and cos (theta + n 2 pi), for n an integer are equivalent. Also note that the principal value of the phase shift is in the range - pi to pi. What is the principal value of the phase shift in radians? You can enter a mathematical expression using pi to represent pi, or a numerical answer.

Solution

Given 0=2F₀₌2*8

F₀ =8 Hz

T=1/F₀ =1/8=0.125 sec= 360 degrees=2 radians

If the signal is shifted by 1.5 sec is nothing but

the S_d=S(t-1.5) shifted by 1.5*2/T=1.5*2/0.125=12*2 =0 radians

i.e zero degrees shifts