To simplify the expression:

0 + 8√54 + 76 + 9/10*√2 - √79 + 21

First, simplify the square roots:
√54 = √(227) = 3√2
√2 = √2
√79 = √(419) = 2√19

Now substitute the simplified square roots back into the expression:
0 + 83√2 + 76 + 9/10√2 - 2√19 + 21

Next, multiply and combine like terms:
24√2 + 9/10*√2 - 2√19

Now simplify further:
(24 + 9/10)√2 - 2√19
(240/10 + 9/10)√2 - 2√19
(249/10)√2 - 2√19
(24.9)√2 - 2√19

So, the simplified expression is:
24.9√2 - 2√19.