Weird system of equations

Question

X : 2 = 7
Y : 2 = 6
X + Y = 15
Find X and Y.

I think maybe this is some unpositional number system. I've tried positional, and it works for basis 21 (if we take X=D, and Y=C), but professor told me that even if that works, it's not solution.

Answer 1

Well, $2$ weird solutions related to "geometrical solution":

Solution 1: suppose we have a circle, and $X,Y$ are certain arcs.
Let measure of arc is the length of corresponding segment.

Image:

And so weird answer: $$ X\approx 12.4428 (\mbox{radius}\approx 7.63599, \mbox{angle}\approx 1.90458) $$ $$ Y\approx 11.0351 (\mbox{radius}\approx 7.63599, \mbox{angle}\approx 1.61503) $$

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Solution 2: in the style of "matches":

$X=7$ matches,
$Y=8$ matches:

(if there are $\ge 5$, then we group each $5$ matches into "square").

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Of course, there can be also solution in "vectors" style.