AM modulation

hi..anyone pls help me with this. have uploaded my am modulation circuit.but quite confused on how to calculate the percent of modulation.The lab manual i am referring states that m = Vmax-Vmin/Vmax + Vmin = Vm/Vc.

i set the Vm = 100mVp,Vc=0.75Vp so i must get m=0.13
however i did not get the same modulation index from the simulation circuit.
this is what i get Vmax=105mVp,Vmin=5mVp so m=0.91

A 741 opamp is 43 years old. It has trouble with frequencies above 9kHz but you are trying to feed it 159kHz.
Maybe your sim program doesn't know it won't work.

In Multisim, try using an LMV851MG, it has a much better frequency response than the 741.