Suppose that geneticists developed a strain of bacteria that breaks down polyethylene, an otherwise non biodegradable plastic. how would such bacteria be useful? do you foresee any dangers from these new bacteria?

Polyethylene is a widely used substance for manufacturing plastic. A bacteria like that could "eat" plastic garbage made from polyethelene which would be really helpful. The danger is that a bacteria can't differentiate between junk and useful things made out of PE, so they would eat everything made from it. 

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is

60.0 - there are 3 significant numbers