Answer:
Let's solve this in steps:
1. Convert mixed numbers to fractions:
```
3 1/2 = 7/2
9 3/4 = 39/4
```
2. Perform the subtraction:
```
7/2 - 39/4 = -11/4
```
3. Divide by -2.5:
```
-11/4 / -2.5 = 4.4
```
Therefore, the value of the expression is **4.4**.