What is 2.8 millimeters written in expanded form?

Expanded form is a way to write a number that shows the value for each place.

susie has 7 apples

1. a^4+8a^3+24a^2+32a+16

2.y^8+8y^7+28y^6+56y^5+70y^4+56y^3+28y^2+8y+1

3.x^6-3x^4y^2+3x^2y^4-y^6