Subtract (5 − 2i) − (1 + 8i). which property allows you to write the expression as 5 − 2i − 1 − 8i?

This is the concept of algebra, we are required to subtract the complex numbers. Thus;
(5-2i)-1(1+8i)
opening the brackets using the distributive property we get:
5-2i-1-8i
collecting the like terms we get:
5-1-2i-8i
=4-10i
the answer will therefore be:
4-10i