Given parameters:
Total length of curtains bought = 20m
She used 8m for the living room
She used 7m for the dining room
unknown:
Quantity used for the kitchen = ?
Solution:
Quantity used for the kitchen = Total length - (living room + dining room)
Input the parameters given solve;
Quantity used for the kitchen = 20 - (8 + 7) = 5m
The length of curtain used for the kitchen is 5m