You have to find the difference in height between both checkpoints. To do this just calculate 196 - 52. Checkpoint 5 is 144 (meters?) higher than Checkpoint 2.
In all right triangles, the ratio between a leg and the hypothenuse is the sine of the angle opposite to the leg.
So, in your case, we have

In order to find XY, we have

So, the ratio for the sine is

Please explain some more:)
Q10 A20 i think
hope this helps