[factoring][section 40]

(1.)  18                here is the problem

          18
          /\
         2  9
           / \
          3   3         make a factor tree

result:  18 = 2*32

(2.)  36                  here is the problem

            36
           /  \
          9    4
         / \  / \
        3  3  2  2           make a factor tree

result:  36 = 22 * 32

(3.)  21                     here is the problem

               21
               /\
              3  7         make a factor tree

result:  21 = 3*7

(4.)  15                 here is the problem

              15
             /  \
            3    5       make a factor tree

result:  15 = 3*5

(5.)  42                here is the problem

 
           42
          /  \
         6    7
        / \
       2   3         make a factor tree

result:  42 = 2*3*7
 

(6.)  45             here is the problem

          45
         /  \
        9    5
       / \ 
      3   3              make a factor tree

result:  45 = 32 * 5

(7.)   49               here is the problem
 
                 49
                 /\
                7  7     make a factor tree

result:  49 = 72

(8.)  25                 here is the problem

             25
            /  \
           5    5     make a factor tree

result:   25 = 52

(9.)  28               here is the problem
                   28
                  /  \
                 4    7
                / \
               2   2     make a factor tree

result:    28 = 22 * 7

(10.)  33                here is the problem

                33
               /  \
              3   11      make a factor tree

result:  33 = 3*11