3) This one is a little different, since you're finding the angle instead of the side. You can denote the angle to be the variable x. Thus:
cos x = 14 / 26
Use a calculator to divide out 14/26, then round to four decimals.
cos x = 0.5385
Now go to the cosine chart and find which angle has the cosine 0.5385. It's a strange problem they gave you, because the chart doesn't have a value that matches it (kind of confusing if you ask me). But you can find two angles it is between. Notice that cos 57° = 0.5446 and cos 58° = 0.5299. Thus, the angle must be between those two. It turns out it is closer to 57°, so you can say:
x = 57°