Break it up into vertical and horizontal components. + denotes vertically up and horizontally right, - denotes vertically down and horizontally left.
Vertical: +3000 N (force A up), -2800 sin45 N (force C down), -2500 sin45 N (force B down). Therefore, +∑ F = -747.666 N
Horizontal: +2800 cos45 N (force C right), -2500 cos45 N (force B left). Therefore, +∑ F = 212.132 N
So, the resultant force is √(-747.6662 + 212.1322) = 777.177 N
The direction is -74.16° below the horizontal.
The answers appear to round the value to the nearest hundred, and they express the angle in terms of compass bearings, but both are the same thing.