Janice had X sentences from yesterday already typed to start with today.
Janice typed 6 * 20 = <<6*20=120>>120 sentences before her break.
She typed 6 * 15 = <<6*15=90>>90 sentences after her break.
She typed 6 * 18 = <<6*18=108>>108 sentences after her meeting.
Therefore, she typed 120 + 90 + 108 = <<120+90+108=318>>318 sentences today in all.
She had to erase 40 sentences, so she had 318 - 40 = <<318-40=278>>278 sentences that she typed today left.
The paper had X + 278 = 536 sentences at the end of today.
Thus, she had X = 536 - 278 = <<536-278=258>>258 sentences typed on the paper to start with today.
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