How many different combinations {ACT}

Natalie has 12 shirts and 7 pairs of pants.  Each shirt can be worn with each pair of pants.  How many different combinations of 1 shirt and 1 pair of pants does Natalie have to choose from?
A.)  7
B.)  12
C.)  19
D.)  42
E.)  84

Forget Natalie, right now.  Here's a similar, more basic example:

A basic example:
how many different ways can the numbers
be matched with the letters, below:

1, 2, 3    A, B 

1A  2A  3A
1B  2B  3B 

3 numbers x 2 letters = 6 ways

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Back to Natalie:

Possibilities for:
12 shirts and 7 pairs of pants
= 12 x 7
= 84 different combinations

E.)


- Algebra House