-2(3.5(4/5) - 2.5) + 4.5(4/5) - 1

First, we simplify the expression inside the parentheses:

= -2(2.8 - 2.5) + 3.6 - 1
= -2(0.3) + 2.6
= -0.6 + 2.6
= 2

Now we substitute this result back into the original expression:

= 2 + 3.6 - 1
= 4.6 - 1
= 3.6

Therefore, -2(3.5у-2.5)+4.5у-1, when у=4\5, equals 3.6.