4.how can you verify euler’s formula for this net of a cube?

This is for any polyhedron that does not intersect itself. The Euler's formula states that the number of faces plus the number of vertices or corner points less the number of edges is always equal to 2.

Faces + Vertices - Edges = 2

A cube has 6 faces, 8 vertices, and 12 edges.

Euler's formula: 6 + 8 - 12 = 2 ⇒ 14 - 12 = 2 ⇒ 2 = 2 ur welcome man 

Look, when you want to do something like put it like x^2. x2 could mean x² or x₂. so to clear confusion, know the notation. to find the product multiply the x's and you get -8x and the y's and you get 6y. since it's all being multiplied it is just -8x6y, or answer a. although the better answer is -48xy(combining -8 and 6) because you should multiply constants whenever you can.