We have $7 + 7 + a = 14$. Since $a$ is a single digit, it must be the case that $a = 0$ and there is a carry-over of $1$ to the tens place.
Now, let's look at the tens place. We have $4 + 2 + y + 1 = 1x$. Since $x$ is a single digit, the sum of $4 + 2 + y + 1$
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