For this case we have that by definition:
[tex]F = ma[/tex]
Where,
We have then:
[tex]F = 10 + 5\\F = 15 N[/tex]
Then, by clearing the acceleration we have:
[tex]a = \frac {F} {m}[/tex]
Substituting values we have:
[tex]a = \frac {15} {5}\\a = 3 \frac {m} {s ^ 2}[/tex]
Answer:
The acceleration of the box is equal to:
[tex]a = 3 \frac {m} {s ^ 2}[/tex]