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.