Atheater has 500 seats. three-fourths of the seats are filled. how many seats are filled?

375 seats are filled

Three-fourths or 3/4 of the seats are taken out of the 500 would be 3/4 = 0.75 or 75% of the seats taken out of the 500 seats in total. 
500 / 75% or 500 * 0.75 = 375 

So, your answer would be that 75% of the seats were taken out of the total of 500 seats. Which would be 375 seats were taken out of 500 seats in total.

Hope this helps. 

~ ShadowXReaper069