Practice with Register (informal vs. formal English vocabulary)

Which word has a more formal connotation?

How would you change the verb in this sentence to make it formal?

We still need to figure out the cause of the problem.

How would you change the verb in this sentence to make it formal?

He left out a lot of information in his presentation. 

How would you change the beginning of the second sentence to make it formal?

We need the report done by tomorrow. Plus, we have to get it approved by Mrs. Kovac. 

Moreover, we have to get it approved by Mrs. Kovac. 

That notwithstanding, we have to get it approved by Mrs. Kovac. 

Therefore, we have to get it approved by Mrs. Kovac. 

How would you change the phrase "SPEED UP" in this sentence to make it formal?

I'm working on a plan to speed up our form-approval process. 

How would you change this sentence to make it formal?

Our product is already popular, but we need to make it widespread. 

Which informal phrase is equivalent to the formal phrase, "We encountered an issue," and sounds like natural English?

Which informal phrase is equivalent to the formal phrase, "I apologize for the misunderstanding," and sounds like natural English?