Steven
Week on starts from Row 3,.


Week Cummulative Run KM Average

1 400 =IF(ISBLANK(B3),"",+B3-B2) =IF(ISBLANK(C3),"",AVERAGE(C$3:C3))
2 850 =IF(ISBLANK(B4),"",+B4-B3) =IF(ISBLANK(C4),"",AVERAGE(C$3:C4))
3 1150 =IF(ISBLANK(B5),"",+B5-B4) =IF(ISBLANK(C5),"",AVERAGE(C$3:C5))
4 =IF(ISBLANK(B6),"",+B6-B5) =IF(ISBLANK(C6),"",AVERAGE(C$3:C6))
5 =IF(ISBLANK(B7),"",+B7-B6) =IF(ISBLANK(C7),"",AVERAGE(C$3:C7))
TOTAL

the answers would be


Week Cummulative Run KM Average

1 400 400 400
2 850 450 425
3 1,150 300 383
4 383
5 383
TOTAL


Best Regards
Aqib Rizvi