Answer:
The expressions are:
2. 
3. 
4. 
Step-by-step explanation:
The given expressions have to be converted into algebraic expressions.
So,
2. Write an algebraic expression for the total number of minutes in h hours and 20 minutes.
Here,
h is a variable that can have any value but the 20 minutes will remain same with any number of hours.
If h is for hour, the number of minutes in h hours will be: 
And there are also 20 minutes so the algebraic expression is:

3. Write an algebraic expression for the total number of hours in 2 hours and x minutes.
In order to convert minutes into hour, the minutes are divided by 60
So converting x minutes into hour means

There are 2 hours already so the expression will be:

4. Write an algebraic expression for the total number of hours in y hours and 45 minutes.
Converting 45 minutes to hours by dividing by 60

The expression is:

Hence,
The expressions are:
2. 
3. 
4. 