The question says this is an upper air contour chart, which gives the height of upper pressure levels derived from both msl pressure and airmass temperature.

The tag "London" tells you it is northern hemisphere and the wind arrow tells you that the low contours are on the left of the arrow (Buys Ballot's law)
If you track back along the contours you find A is on a higher contour line than B, so true height, which is what contours show, is higher at A.
Flying "on the contour chart" means you are flying at a constant pressure level, 500mb, 300mb or whatever the chart is drawn for.

The altimeter setting given, 1013.2, is irrelevant. If you fly at a constant pressure setting, whatever it is, toward low contours you are going down, toward high contours, up.