Up to isomorphism , how many additive abelian groups G of order 16 have the property that x + x + x + x 0 .?

What does it mean by up to isomorphism?

That notation potential to take g(x) and positioned it in for x interior the f(x) equation. So in f(x) x + a million, i visit throw out the x and put in 2x^2 - 3 {f o g}(x) 2x^2 - 3 +a million Simplify. {f o g}(x) 2x^2 - 2