The formula for unit rate is blank over blank = x over one. She types 496 words in 8 minutes, otherwise said "496 words per 8 minutes", which means its 496 over 8. If you do cross multiplication, 496*1 = 496 (Obviously) and 8*x = 8x.
Now, you have 496 = 8x. To isolate the variable, do the opposite of what it says 8x divided by 8 = x. Of course, you have to do the same thing on both sides. 496 divided by 8 is 62. so the unit rate is 62 words per minute.