2

x2

-

x

p

The general term of) 6 expansion is Tr+ 1=

C

r

six

(

2

x2

)6-r(-

x

p

)r=(-

1

p

)r26-r

C

r

six

x3r- 12

Let 3r- 12=0 to get r=4.

Therefore, an item without an X is (-

1

p

)422

C

four

six

∴(-

1

p

)422

C

four

six

=

20

27

The solution is p=3.

So the answer is 3.