If x and y are positive integers such that (3x + 7y) is a multiple of 11, then which of the followings are divisible by 11?
Choose the correct choice from the following answers:
A) 9x + 4y  B) x + y + 4  C) 4x - 9y  D) 4x + 6y  E) None of these
Explanation :   By hit and trial method, we get x=5 and y=1 such that 3x + 7y = 15 + 7= 
<gadget id="calculator">15 + 7</gadget>
<output>22</output>
22 is a multiple of 11.   Then   (4x + 6y)= (4 × 5 + 6 × 1) = 26 which is not divisible by 11   (x + y + 4) = (5 + 1 + 4)= 
<gadget id="calculator">(5 + 1 + 4)</gadget>
<output>10</output>
10 which is not divisible by 11   (9x + 4y)= (9 × 5 + 4 × 1) = 49 which is not divisible by 11   (4x - 9y) = (4 × 5 - 9 × 1) = 20 - 9= 
<gadget id="calculator">20 - 9</gadget>
<output>11</output>
11 which is divisible by 11. Answer : Option 4x - 9y
<result>C</result>
If x and y are positive integers such that (3x + 7y) is a multiple of 11, then which of the followings are divisible by 11?