Answer
The percent mass of Carbon in Capsaicin is about 70.82%.
Work Step by Step
Molar mass of C18H27NO3:
C: 12x18 = 216
H: 1x27 = 27
N: 14x1 = 14
O: 16x3 = 48
216 + 27 + 14 + 48 = 305g per Mol
Percentage of C mass in Capsaicin:
$\frac{216}{305}$ x 100% = 70.82%