¡no tarde!
a. lea b. llegue c. den

First of all, this is a negative sentence. Negations using no is the most basic type of Spanish verb negation. To make a sentence negative, just place the word no before the conjugated verb. So the conjugated verb here is llegue that comes from the verb llegar and is its conjugation that matches the subject pronoun usted (formal you) in the imperative mood. Sentences in this mood are commands, so this sentence is a command. Finally:

¡No llegue usted tarde!