Question

I got a new book. I felt happy.
( Join into a simple sentence)

Answer 1

The given two sentences can be joined into a Simple Sentence in the following manner:

I felt happy on getting a new book.

or

Getting a new book made me feel happy.

Explanation:

A Simple Sentence is a sentence with one subject and one verb only. 

A COMPOUND SENTENCE is a sentence that is made up of two or more independent clauses. There are no dependent clauses in it. The independent clauses in a compound sentence are joined by coordinating conjunctions such as ‘or’, ‘and’ or ‘but’. For example, I really wanted to play the match, but I was too sick to stand even. 

A complex sentence has one independent and one or more dependent clauses. The clauses in a complex sentence can be in any order. If the dependent clause is first,  a comma is usually after it. For example, I hope that I will pass the test.

Answer 2

I was happy to get a new book.

A simple sentence has only one clause. A compound sentence has two or more independent clauses. A complex sentence consists of at least one independent and one dependent clause.

Some important requirements for a simple sentence are:

i. It should have a subject and a verb.

ii. It should express a complete thought.

iii. It should have one clause.