If she bought a 500 pages book and wrote on 150 pages, the number of empty pages remaining is 500-150 = <<500-150=350>>350 pages.
She then wrote on 30% of the remaining empty pages on the second week, a total of 30/100*350 = <<30/100*350=105>>105 pages
The number of remaining empty pages is 350-105 = <<350-105=245>>245 pages.
When she spilled coffee on the remaining empty pages, the number of damaged pages was 20/100*245 = <<20/100*245=49>>49
The number of empty pages remaining that she could write on is 245-49 = <<245-49=196>>196 pages
#### 196