Respuesta :

Answer:

2

Step-by-step explanation:

[tex]\frac{a+b+c}3}= 4\\[/tex]

multiply both sides by 3

a+b+c=12

substitute the values we have

1+9+c=12

10+c=12

-10     -10

c=2

so the third number is 2

hope this helped you !