Answer:
1
Explanation:
Given: 15 decreased by six times a number is -9.
Lets assume the number be "x".
Now, putting the value in the equation to get the number.
six times a number = 6x
Then, 15 decreased by six times a number=

Now,

Adding both side by 15
⇒
⇒

Cross multiplying
∴ x=

Hence, the required number is 1.
Next subtituting the value in equation to check.

⇒

⇒

∴
