Yes, a full suspension mountain bike is worth it if you plan to ride on rough terrain or do downhill riding. The rear shock absorber allows for a smoother ride and better control over technical terrain, reducing fatigue and the risk of injury. Full suspension bikes also offer more comfort, making them ideal for longer rides. However, they can be heavier and more expensive than hardtail bikes, so it is important to consider your needs and budget before making a purchase.

To blow up mountain bike tires, you would need a bike pump. First, remove the valve cap on the tire and unscrew the valve cap. Then, attach the pump head to the valve and begin pumping. Keep pumping until the tire is firm and visually looks full. Be sure to check the recommended pressure range for your specific tire to prevent over-inflating.

To replace a rear derailleur on a mountain bike, you need to first remove the old derailleur by unscrewing it from the derailleur hanger. Then, install the new derailleur by aligning it with the derailleur hanger and tightening it with the appropriate bolt. Next, adjust the limit screws and cable tension to ensure smooth shifting. Finally, test the bike and make any necessary adjustments until the shifting is working properly.