hey,

i hope you are well

the aggregate of PCB marks means you need to calculate the percentage of your three subjects that are physics , chemistry and biology together , let say if you have scored 70 marks in chemistry out of 100 , 60 marks in physics out of 100 and 80 marks in biology out of 100 , then your PCB aggregate will be the sum of total marks obtained in all three subjects that is 210 divided by 300 and multiplied by 100

= [210/300]*100

= 70%

as you have mentioned you have obtained a total of 150 marks out of 300 then your PCB aggregate would be 50 percent.

hope this is clear now!