First, perform the multiplication inside the parentheses:
204 • 405 = 82420

Now, add 137640 divided by 4:
137640 ÷ 4 = 34410
82420 + 34410 = 116830

Next, divide 454500 by 50:
454500 ÷ 50 = 9090

Finally, subtract the result of the division from the sum we calculated earlier:
116830 - 9090 = 107740

Therefore, (204•405+137640:4)-454500:50 = 107740.