If 21 more than 3 times a number is - 15, what is the number?

The number is - 12.

Step-by-step explanation:

3x+21=-15

3x=-15-21

3x=-36

x=-36/3

x=-12

-12

Step-by-step explanation:

let the number be x

"3 times a number" : 3x

"21 more than 3 times a number" : 21 + 3x

"21 more than 3 times a number is - 15" : 21 + 3x = - 15

Solving this equation:

21 + 3x = - 15 (subtract 21 from both sides)

3x = - 15 - 21

3x = - 36 (divide both sides by 3)

x = - 36/3 = - 12