Rectification of errors !!!

Dear Friends,

Please answer these doubts of accounts-Rectification of Errors.Its really important for me.

Rectify the following errors: 

1. An amount of Rs.375 has been posted on the debit side of commission account instead of Rs.275.

2.Goods of Rs.200 purchased from Sohan Lal has been posted to his account as Rs.250.

3.Total of Sales Returns Book was overcast by Rs.475 

4.Goods of Rs.300 were sold to Mahesh,but it was recorded in Purchase Book.

I need rectifying entries and accounting effect for the same above entries. 

Thanks in advance.:):):)