what is the sum of a and b?

Answer:
a=13, b=7
Step-by-step explanation:
You can use the exponent rule
[tex]3x^{a-5}y^{9-b}=3x^{8}y^{2}[/tex]
so [tex]x^{a-5}=x^{8}[/tex] so
a-5=8
a=13
[tex]y^{9-b} =y^{2}[/tex] so
9-b=2
b=7