慢多了（Adj.+degree complement） "much slower" 
   
    A degree complement is not always registered as an actual amount. It always appears after the adjective or verb it complements to show degree or extent.
 
                     Subj.+ Adj./V+(得) + Complement
Examples:
1. 这家工厂的生产效率低极了。
The production efficiency is extremely low in this factory.
2. 海运比空运慢多了。
Sea shipment is much slower than air transport.

Substitutive drills: