I'm in Suffolk, so don't expect me to know the geography of Sunderland too well ;-)
However, web-searching for 'Sunderland business park' suggests that 'Doxford International' might be where your son is trying to get to. If so, service 71 will take him from Chester-le-Street to Houghton-le-Spring Broadway.
From there he can take an X3 into the business park or an X35 to Doxford Park (Monarch Avenue) which is a very short walk away. The total journey time is just under an hour.
A slightly quicker route (around 45 minutes), but with possibly fewer useful connections, is to take the X8 to Washington Galleries bus station and then the 169 to the business park.
This information is derived from the route planner, here:
http://217.23.229.206/jpclient.exe
An alternative source of information is to phone Traveline on 0870 608 2 608.
Chris