Please explain I don't get it don't you subtract the fractions ??

Answer:
-1/2 y + 3
Step-by-step explanation:
The problem is not the fractions. They're fine. 2/5y - 9/10y = -1/2y
The problem is the 11
- 4 + 7= 3 not - 11
The correct result should be -1/2 y + 3