So, first you have to put the amount of decrease/increase over the original amount. (like a fraction!) then you are trying to find the percent so you would do x over 100. so it would look like; 438,000 x
----------- = -----
561,000 100
Then you would cross multiply (438,000 times 100 and 561,000 times x [which would be x]) and it would look like; 43,800,000 = 561,000x
(a shortcut for 0's is that if theres the same amount of them on each side just cross them out! It gives you the same amount every time!)
43,800=561x and finally you would divide 43,800 by 561 and your answer is 78.07%
Hope I helped! :)