-3/4 + 8.5(0.021 ÷ 0.01 - 2.51)

First, we need to simplify the expression inside the parentheses:
0.021 ÷ 0.01 = 2.1
0.021 ÷ 0.01 - 2.51 = 2.1 - 2.51 = -0.41

Now we substitute this back into the original equation:
-3/4 + 8.5(-0.41)

Next, we multiply 8.5 by -0.41:
-3/4 + (-3.485)

Now we add the two terms together to get:
-3.485 - 0.75 ≈ - 4.24

Therefore, -3/4 + 8.5(0.021 ÷ 0.01 - 2.51) ≈ -4.24