Validation Expression [start with 8 or 9 And 8 digits only]

hi, friends,

I want to use regular validation expression. but I don't know the validation expression for my requirement.

my requirement of validation is:

Number must start with 8 or 9 And it has 8 digits only. it is for phone number, so must be digits.

must have 8 digits only and start with 8 or 9.

so, 81011111, 92522222, 82033333, 92455555.....are valid.

8111111, 9333333, 22222222, 89111 are not valid.

pls share me validation expression

regard.