Answer:
This is a often mistake when being asked to write an expression. The words "is less than" and "less than" have different meaning. The phrase, "is less than" means 6 < k. The phrase "less than" means 6 - k.
I'll make a example with your problem. (I am adding a "x" on it cause it's easier for me to interrupt. But means the same as yours.)
"10 less than a number x"
10 - x
"10 is less than a number x"
10 < x
