How to write 3+0.7+0.04 in standard form

Place them accordingly, the decimal point will always stay between the 3 and the 7. So it would come out as 3.74 

3.00 + 0.70 + 0.04 the numbers fall right in place

You have to consider the sample space. In this example the sample space 
is {1,2,3,4,5,6}
A simple event can be defined as a SINGLE outcome : Example getting a 3 OR 5 OR any other number from the sample space.
Now if you roll 1 dice & you want to get an even number (2,4,6) then you have chosen from the sample space 3 outcome & this is a compound event
Equally if you roll 2 dice and want to get "one" and/or "three" this is a compound event since you have chosen 2 outcome from the sample space.
Mind you, if you want 5 And 5 when rolling two dice it's a simple event because you have chosen ONE outcome from the sample space.
Hope this will help you to understand this kind of problem