It's estimation, so, you don't actually have to solve the problem completely. Let's take a look at the first problem:
38 + 46 =
So, first, you would round the numbers up, and since the number's in the 'ones' place are higher than 5, you would round them up, if the number's in the 'ones' place is lower than 5, then round them down.
So, now your equation would be, 40 + 50
Your answer would be 90.
I hope this helps!