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Explanation:

Let CP = 100
Current gain = 20
⇒ SP = 120
CP = Cost of A + Cost of B + other
      =      30%    +    50%     +   20%

Since cost of German mark (A) increase by 30%
New cost of A = 30 + 30% of 30 = 39
Similarly
New cost of B = 50 + 22% of 50 = 61
New CP = 39 + 61 + 20 = 120
New SP = 120 + 10% of 120 = 132
Maximum profit = $\frac{12}{20}=10\%$