A14x
Since you can just add them together, because both of them have x .
So it turns into / you can think it as this way
(i'm not sure if you learned this yet but it's called factorization)
(you're gonna learned it in the future)
5x + 9x
= x(5+9) *this step help you understand better :)
= x14
= 14x
Hope I can help you :) Good luck in math
