The first three cash prizes sum to $200 + $150 + $120= $<<200+150+120=470>>470
The remaining amount of cash prizes to be distributed is $800 - $470= $<<800-470=330>>330
The number of novels left to be awarded is 18 – 3= <<18-3=15>>15 novels
So each writer from 4th to 18th will earn $330 / 15= $<<330/15=22>>22
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