–1.8 – 3.9 =

-1.8 - 3.9 = -5.7

To subtract -1.8 from 3.9, follow these steps:

Step 1: Rewrite the equation with the numbers in place:
3.9 - 1.8

Step 2: Subtract the numbers:
3.9 - 1.8 = 2.1

So, -1.8 - 3.9 equals 2.1.