Respuesta :

mtn021

Answer:

15

Step-by-step explanation:

3a+b=54

3a+9=54

54-9=45

45 ÷ 3= 15

3 × 15 - 9=54

45 + 9=54
15 because the first thing you have to do is plug in 9 so the equation would then be
3a +9 = 54, then you would subtract 9 from both sides and then you would get 3a = 45 and then divide both sides by 3 and you would get a= 15