There are 2 ways to reason this question.

(a) As suggested by the hint the concentrations are halved:
A1 = e1c1l1 = 4200 X 1.50X10-4 X 1 = 0.630
A2 = e2c2l2 = 4200 X 1.30X10-4 X 1 = 0.365
A = 0.630 + 0.365 = 0.995

 (b)Alternatively you could think of the 1 cm cell as being 1/2 cm of the 1st solution and 1/2 cm of the 2nd solution.
Therefore A = 1.00/2 = 0.995 as before.

In either case:
A = 0.995 = log I0/I
I0/I = 9.89
%T = 100 I/I0 = 100/9.89 = 10.1%

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