How do you know when to rewrite square trinomials and difference of squares binomials as separate factors? How can sums and differences of cubes be identified for factoring?

The first week samantha learned to read braille, she could read 10 words per minute. in the second week she increased her speed by 20%. in the third week she increased her speed again by another 25%. how many words could she read per minute by the third week? hurry and tell me!