Answer:Take the alternating sum of the digits in the number, read from left to right. If that is divisible by 11, so is the original number. So, for instance, 2728 has alternating sum of digits 2 – 7 + 2 – 8 = -11. Since -11 is divisible by 11, so is 2728.
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The triangle have three sides and draw the sides
We have two numbers say a, b. And a system of equations.

It looks a bit intimidating but it's actually very easy.
Instead of term a + b in the second equation we can say it's zero because the first equation describes a + b as being equal to 0.
So,

The above equation is not true therefore numbers a and b do not exists in the real number domain.

No solution.
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The answer is 7 1/15