Replying to English mark

Before u roast, it's grade 10 English I handed in like 1 thing..

Ok so my in class mark is worth 70%, my ISU is worth 15% and my exam is worth 15%.

My friends think it works by average... But wouldn't it work like this:
56%(my mark) of 70
75%(my ISU mark) of 15
X% of 15

Add those up and it's my final mark?
I'm just trying to figure out what I need on the exam to pass...