Well, when you multiply fractions, you treat the numerators (top number) and the denominators (bottom number) separately. And then put them back together as one whole fraction. Let's look at them:

13. 6 * 2/5

Can be rewritten as:

6/1 *2/5

We can separate the numerators:

6 * 2 = 12 <--- That is our new numerator

Same with our denominators:

1 * 5 = 5 <--- That is our new denominator

If we put those together, we get:

12/5

14. 5 * 3/7

Using the same process:

5/1 * 3/7

5 * 3 = 15 <-- New numerator

1 * 7 = 7 <-- New denominator

Giving us:

15/7

15. 5 * 2/11

5/1 * 2/11

5 * 2 = 10

1 * 11 = 11

Giving us:

10/11

16. 2 * 2/5

2/1 * 2/5

2 * 2 = 4

1 * 5 = 5

Giving us:

4/5

17. For this one we must switch the mixed number 2 1/2 into an improper fraction, and how we do that is this:

We take the denominator and multiply it by the whole number:

2 * 2 = 4

We then take that answer and add the numerator to it:

4 + 1 = 5 <-- Our new numerator

Making our fraction:

5/2

So our problem is rewritten like this:

5/2 * 3/4

We solve like normal:

5 * 3 = 15

2 * 4 = 8

Giving us:

15/8

18. Same thing here:

4 * 2 = 8

8 + 1 = 9

Giving us: 9/4

9/4 * 3/5

9 * 3 = 27

4 * 5 = 20

Giving us:

27/20

19. 1 1/2 = (2 * 1 + 1) /2 = 3/2

3/2 * 3/7

3 * 3 = 9

2 * 7 = 14

Giving us:

9/14

20. 1 1/3 = (3 * 1 + 1) /3 = 4/3

4/3 * 4/5

4 * 4 = 16

3 * 5 = 15

Giving us:

16/15

Thus your answers are:

13. 12/5

14. 15/7

15. 10/11

16. 4/5

17. 15/8

18. 27/20

19. 19/4

20. 16/15

I hope that helped.