During his entire school life, John’s average marks in science was 80% and his average marks in mathematics was 90%. If his combined average marks in science and mathematics was 84%, while the total marks obtained by him in science was 54,000, what was John’s total marks obtained in mathematics?

36000

Let marks in Science = 3x   & Marks in Maths 2x

3x = 54000 (given)

1x = 18000

2x = 36000

John's marks in Maths = 36000