Since the ratios are 4,3, and 8, the best way to do it is to use a proportion.
So yeah what you do it cross multiply and get 120=8x divide by 8 and get 15. 15 ounces of walnuts.
Now for total just find the last part. Since 4 is half of 8, the number of ounces is half of 40, which is 20. So 20+40+15? You guessed it 75 ounces of Granola.