Firstly :
Pour all the water from 8oz to 3oz and 5oz. Right now, the breakers of 3oz and 5oz should be full to brim.

You would have :
3oz beaker- 3oz water
5oz beaker- 5oz water
8oz beaker is empty

Secondly :
Pour all the water from 3oz to the 8oz beaker.
(8oz beaker have 3oz water now)

Then using the 5oz beaker’s water, pour into 3oz beaker up to its brim.
(5oz beaker left 2oz of water, 3oz beaker has 3oz of water now)

You would have :
3oz beaker- 3 oz of water
5oz beaker- 2oz of water
8oz beaker- 3oz of water

Thirdly :
Pour all the water from 3oz beaker(2oz water) to 8oz beaker(3oz +3oz = 6oz of water). 8oz beaker should have 6oz of water now.

Take the 5oz beaker (2oz water) pour into 3oz beaker(empty). Making your 5oz beaker empty, and having your 3oz beaker with only 2oz of water.

You would have :
3oz beaker with only 2oz water
5oz beaker is empty
8oz beaker with only 6oz of water

Lastly :
Take your 8oz beaker which contains 6oz water pour into 5oz beaker. (5oz beaker full of water, 8oz beaker left with only 1oz water)

Note: 3oz beaker has only 2oz of water. This means you can pour another 1oz of water to make it full.

Use 5oz beaker to pour some water into 3oz beaker to make it full.

Right now you should have :
3oz beaker- 3oz water
5oz beaker- 4oz water
8oz beaker- 1oz water


Let me know if you couldn’t understand.