Here we go, Evelyn. Hopefully this answer will help you with the others!
Let's let m = the number of months.
If I quit before 30 months, I get no bonus, so I receive $1850m
If I quit after 30 months but before 60 months, I receive $1850m + 30(250), because I get the first 30 months of bonus.
If I stay 60 months, then I get $1850m + 60(250).
I'm not sure how to type the big { so imagine it's there.
f(m) = $1850m if m < 30
$1850m + $7500 if 30 < m < 60
$1850 + $15,000 if m = 60
Hope this helps!