It looks like for all of these we will be using the Pythagorean theorem.
If you don't know what this is or how to apply it, go to the website "Khan Academy" and watch his video(s) on it. I would suggest going to that site whenever you don't understand something in math :)
I'll just be giving you the answers and won't explain what I'm doing, but please do go to Khan Academy to find out how to do it on your own!!
Anyway, onto the answers.
1) a = 12.5, b = 5.7, c = 13.7.
2) 24
3) 19.2
4) 6.4
5) 18.7
6) 98.5
7) 1.9
Hope this helps!!!