Getting new mean from all given data

I have 3 homework questions here, sorry for it maybe a bit long but I am stuck at how to find a new mean value for Q1 part 2, Q2&3 part b
It has numerical answers for Q1, they are 0.11% and 8.23% for part 1 and 5.02mm for part 2.
In Q2 (a plastic strips), my numerical answers for part a is 0.466% and 2.28%.
In Q3, 0.621% for both need to be scrapped and reworked.
I have no idea where should I start, please help:shakehead