Un
Re
-ful
-ist
pre
100

Untie

not tie(d)

100

rewrite

write again

100

forgetful

full of forgetting 

100

artist

person who does art

100

preheat

heat before

200

unlock

not locked 

200

redo

do again
200
thankful

full of thanks 

200

scientist

person who does science

200
preteen

before teen

300

unfair

not fair 

300

reread 

read again

300

painful

full of pain

300

guitarist

person who plays guitar 

300

premake

make before 

400

unhappy

not happy

400

retest

test again

400

careful

full of care 

400

therapist

person who does therapy 

400

preschool

before school

500

untrue

not true 

500

rebuild

build again

500

hopeful

full of hope

500

violinist

person who plays violin

500

prewash

wash before