Let's factor m2 + 16m + 64
The middle number is 16 and the last number is 64.
Factoring means we want something like
(m+_)(m+_)
We need two numbers that...
 Add together to get 16
 Multiply together to get 64
Can you think of the two numbers?
Try 8 and 8:
 8+8 = 16
 8*8 = 64
Fill in the blanks in
(m+_)(m+_)
with 8 and 8 to get...
(m+8)(m+8)
Answer:
(m+8)(m+8)