Hi. I worked from the inequality towards something I know is true and then rewrote the proof in the correct direction.

It's a bit clumsy but here's how I started.

similar for b and c.

add three of those together to get

Now add 2 to both sides and ask yourself what is another way to write etc and what is another way to write 1?

I'm a bit rushed just now.

Ask if you need more hints.