The park's length is 21 meters, and the width is 45 meters. An additional jogging track is to be built around the park, which is 15 meters longer than the combined length and width of the park. After completing the jogging track, the city plans to build a bike track around the jogging track. If the total length available for the bike track is 90 meters, how much shorter would the bike track be compared to the available space?