Tyla is simplifying the expression 6 - 2x + 5+ 4x here is their work:

6-2x+5+4x
(6-2)x+ (5 + 4)x
4x + 9x
13x

a)How is Tyla's work incorrect? Explain

b) Simplify the expression 6 - 2x + 5 + 4x:
pls help asap ​