Answer:
-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
