Answer:
Compound.
Step-by-step explanation:
The sentence is a compound sentence because it is formed of two separable sentences:
"My brother practices drums every day. He is improving."
When a sentence consists of two or more independent clauses (think: potential sentences on their own), it is a compound sentence.
A simple sentence contains only one independent clause.
A complex sentence is a dependent clause and an independent clause together.
Hope this helps!