I'll jump in with both feet.......
Assuming 30 feet per millibar.
QNH at 'A' is 1020
QNH at 'B' 998, so that's 22 Millibars less which would translate into an overread of 660 feet if both airfields were at same height. Altimeter would therefore read 1260 feet.
But 'B' is 300 feet lower than 'A', so the sltimeter would actually read 960 feet on arrival at 'B'.
SSD