A box contains 4 red pencils and 6 black pencils

You would add up all the pencils to get yiur denominator, so the denominator would be 4+6=10. Since there is 4 red pencils, 4/10 of the pencils are red. To get an equivalent fraction, you can divide by 2. 4 divided by 2 is 2. 10 divided by 2 is 5. So one of your equivalent fractions would be 2/5. To get your second equivalent fraction you have to multiply because 5 is prime and cannot be divided by anything but itself and 1. 10X2=20 and 4X2=8. So your second equivalent fraction could be 8/20.

If this makes it easier here is the final equation.

4/10=8/20=2/5