I'm not quite understanding how to solve these word problems

I'll help you on the first one.
Anya test scores are 78 and 91.
She has one more test and want to average between an 80-89 inclusive.
Lets set up a inequality and call the remaining test x.
80<=(78+91+x)/3<=89
Multiply everything by 3
240<=169+x<=267
Subtract 169 from everything
71<=x<=98
In interval notation that would be [71,98]
In set notation that would be{x|71<=x<=98}
For the graph, I don't really understand. I think you just graph 71<=x<=98.

Annihilation

Step-by-step explanation:

Lena, a biologist and former soldier, joins a mission to uncover what happened to her husband inside Area X -- a sinister and mysterious phenomenon that is expanding across the American coastline. Once inside, the expedition discovers a world of mutated landscapes and creatures, as dangerous as it is beautiful, that threatens both their lives and their sanity.

Release date: February 23, 2018 (USA)

Director: Alex Garland

Music by: Ben Salisbury; Geoff Barrow

Adapted from: Annihilation

Box office: $43.1 million

Cinematography: Rob Hardy