Right answer is (a) 820.68kg
Best explanation: Given, length L=12m
Now, length is given by,
L = a*W0^c
Now, for jet transport aircraft a=0.67, c=0.43
Hence, take-off gross weight is W0^c = L/a
W0^0.43 = 12/0.67 = 17.91.
Now by taking log at both side,
0.43*ln W0 = ln17.91 = 2.885
lnW0 = 6.710
Hence, by using antilog,
W0 = e^6.710 = 820.68kg.