```ts
export function tilesAcross(length: number, tile: number): number {
  return Math.ceil(length / tile);
}

export function tilesNeeded(width: number, height: number, tile: number, spare: number): number {
  let totalTiles = width * height;
  const spareTiles = Math.floor(totalTiles * (spare / 100));
  const completeRows = totalTiles / tile + Number.isInteger(totalTiles % tile);
  return completeRows + spareTiles;
}
```