What is the area of the semicircle?
"semi" is a DERIVATIONAL affix meaning 'half', it changes the meaning of the word (picture a circle and a semicircle - different!)
Don't let your muscles atrophy.
"-trophy" is a DERIVATIONAL affix meaning "a-" meaning 'without' and root "trophy" meaning
We danced all night.
"-ed" is an INFLECTIONAL affix, making the sentence past-tense.
I think it's annoying when someone interjects when I'm talking.
"inter" is a DERIVATIONAL affix meaning 'between'. It changes the meaning of the root 'ject' which means "to throw"
That was the hardest test ever!
"-est" is an INFLECTIONAL affix making the root superlative
That suitcase was cumbersome.
"-some" is a DERIVATIONAL affix meaning 'characterized'. cumber='hinder'