Good morning, Dalyia!
The first thing you should do is mark these three points on a graph, just so you have a visual of what you're working on. After you've plotted the points, draw a line from C to (-2,0), then a line from (-2,2) to B. Notice you have two right triangles now.
Now, let's work on the smaller triangle first. If you count the units for the sides of the triangle not including the hypotenuse, you'll see the vertical side is 4 units, and the horizontal side is 4 units, as well. Knowing that, we can use the Pythagorean Theorem to find side BC (a^2+b^2=c^2). So, if we plug in our sides, we have 4^2+4^2=c^2 => 32=c^2 => c=6. Line BC is 6.
The same can be done for line AC. The sides of that triangle are 6 units each, so: 6^2+6^2=c^2 => 72=c^2 => c=8.49. Thus, side AC is 8.49.
All you have to do now is set up the ratio as asked, which is the lengths of side BC to AC, which makes 6:8.49, or 6/8.49.
Hope this helps!