Checking subtotals with varying entries

Hi,

Please see attached.

Entries in column B indicate a new entry. What I need to do is to check that the sum of values in column G equal the corresponding value in column B. So, Entry B is incorrect for example, as 40,20 & 30 does not equal.

In the real example, here are hundreds of enties. Each entry has varying numbers of rows.

Any assistance would be great.

Thanks.