Team X: $20$ overs → $N$ runs.

Team Y ties in $10\%$ fewer overs → $18$ overs, so Y’s actual run rate = $N/18$ runs per over.

If Y’s run rate were $50\%$ higher: new rate = $1.5 \times (N/18) = N/12$ runs per over, so in $12$ overs Y would score $(N/12) \times 12 = N$ runs.

This condition holds for any $N$ and gives no additional constraint. Therefore, $N$ cannot be determined from the given information.