A number decreased by 15 is the same as 3 times as much as the number increased by
1.

-4

Step-by-step explanation:

We create an equation like this n-15=3n+1

We need to subtract 3n on both sides to get -4n-15=1

Next, we need to add 15 on both sides to get -4n=16

Divide 4 on both sides to get -4.