%T = 100I/I0 = 85

I/I0 = 0.85

I0/I = 1/0.85

A1(for 1 cm) = log(I0/I) = log(1/0.85) = 0.0706
 

Since A = e cl amd e and c are constant then A2(for 3 cm) = 3.0X0.0706

= 0.2117 = log(I0/I2)

I0/I2 = antilog 0.2117 = 1.628

%T = (I2/I0)100 = 100/1.628 = 61.4%

Answer is B

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