Calculate the subtraction (8.5−1.8i)−(−1.3+2.7i)

To perform the subtraction \((8.5−1.8i)−(−1.3+2.7i)\), we can rewrite it as:

\[ (8.5 - 1.8i) + (1.3 - 2.7i) \]

Now, we can combine the real and imaginary parts separately:

1. Real Parts: \(8.5 + 1.3 = 9.8\)
2. Imaginary Parts: \(-1.8 - 2.7 = -4.5\)

So, putting it all together, we get:

\[ 9.8 - 4.5i \]

Thus, the final answer in the form \(a + bi\) is:

\[ \boxed{9.8 - 4.5i} \]