Çözüldü Numbers and Digits

If ab, which is a two-digit natural number, is seven times the sum of its digits, how many times is the natural number ba the sum of its digits?

A) 2
B) 3
C) 4
D) 5
E) 7

ab = 10a + b = 7(a + b) ⇒ a = 2b
ba = 10b + a = 10b + 2b = 12b
12b = k·(b + 2b)
4 = k.

Source: Student Selection and Placement System, Mathematics Question Bank, Zafer Press, 7th. Ed., December 1998, Page 11, Test 1, Question 1

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