If you had an infinite supply of water and a 5 quart and 3 quart pail, how would you measure exactly 4 quarts?

fill cup5 , pour it in cup3, cup5 left with 2quarters.
pour out cup3, pour cup5 into cup3, cup3 has 2quarters.
fill cup5, pour it in cup3 until cup3 fills
now cup5 has 4quarters.