The total amount of words in 15 pages will be
350 * 15 = 5,250
She can type 70 words per minute, now how about per hour? Each hour has 60 minutes so we calculate to find out the total amount of words she can type per hour.
This will be 70 * 60 = 4,200 words
Now we calculate how many hours it will take to type 5, 250 words.
1 hour = 4,200
x = 5,250
where x is the time in hours needed to type 5,250 words.
We cross multiply the equation:
4,200 * x = 5,250 * 1
4,200x = 5,250
x = 5,250/4,200
x = 1.25
She will need 1 and a quarter hours to type her paper.