Question on Modulus of Elasticity of concrete in STAAD

Hello. How does STAAD compute the modulus of elasticity of concrete (default material properties)?

The default values are:

fcu is 27.58 MPa

E is 21728 MPa

Say I would like to use f'c = 27 MPa, what would be the corresponding E and fcu?

I know that f'c is about 0.8fcu.

Thank you!