The best way to achieve an accurate measurement is to draw out your driveway and then divide it up into sections.
To get the sq.m of each section simply calculate the width x the length:
8m x 4m = 32 sq.m
3m x 6m = 18 sq.m
For more awkward shapes like Area C just simply do the same width x the length but also divide by 2:
3m x 2m = 6 sq.m ÷ 2 = 3 sq.m
Total Driveway Area:
A + B + C = 53 sq.m