6 + 4 x 7 - 2 = ?

     We multiply the 4 and 7 to get 28 first. Then we can rewrite the
     problem like this:
  
     6 + 28 - 2 = ?

     At this point it doesn't really matter which operation we do
     first, but we will solve the problem left to right since that
     is the usual way of solving the problem.

     First we add 6 and 28 to get 34 and then we subtract 2 from 34
     and get 32. 

   5 x 5 - 3 x 2 = 

   We need to solve the two multiplication parts of the problem
   separately. We get 5 x 5 = 25 and 3 x 2 = 6. Then we subtract
   our products in the order they are presented in the problem.

   25 - 6 = 19

   We could diagram the problem like this:

   5 x 5 - 3 x 2 = 
    \ /     \ /
    25   -   6   =  19

   9 - 3 + 2 x 4 = 

   First we find the product of 2 x 4 and then we can re-write
   the problem like this:

   9 - 3 + 8 = 

   Then we subtract 3 from 9 to get 6 and then add 8 to 6 and get
   our final answer of 14.