First you need to simplify each of the fractions as follows:
14/21 = 2/3
12/21=4/7
After that, to multiply them, just multiply the top digits with each other and the bottom digits with each other:
2*4=8 and 3*7=21 so the end result is 8/21.
so (14/21)*(12/21)= 8/21
