My maths teacher gave me this equation and I really don't know how to solve this: $$\overline{abc}+\overline{ab}+\overline{bc}+\overline{ac}+a+b+c=29,$$ where $a$, $b$, $c$ are digits.
I need to find how many three digit numbers are there which satisfy this.
You have three equations in three unknowns. From the least significant digit (take the rightmost digit of each term) you have
$$c + b + c + a + b + c = 9$$
From the next digit you have $$b + a + b + a = 2$$
From the most significant digit you have $$a = 0$$ noting that $29 = 029$.
Can you take it from here?