Question

O triplo de um numero subtraído de 12 é igual a 21

Answer 1

$3x-12=21\\\\\\ 3x=21+12\to\\\\ 3x=33\to\\\\ x= \frac{33}{3} \to \\\\ x=11$


$Verificando:\\\\ 3*11-12=21\to\\\\ 33-12=21\to\\\\ 21=21$

Answer 2

3x - 12 = 21
3x = 21 + 12
3x = 33
x = 33/3
x = 11