[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