I worked out the first problem because I knew the peanuts were double the amount of cashews and there are 8 cashews so 2x8=16,so there are 16 peanuts in Rachel's bag.
For the second problem there are two cashew nuts for every three peanuts, and there are 12 peanuts in total,3x4=12 so 2x4=8. This means that there are 8 cashew nuts in Marianne's bag.
Because Rachel and Marianne mix their nuts together, there are 16 peanuts in Rachel's bag and 12 peanuts in Marianne's bag, so 12+16=28. Also in Rachel's bag there are 8 cashews then in Marianne's bag there are 8 cashews as well, so 8+8=16.
So the ratio is 28:16 ,however you need to make this into its simplest form. You do this by dividing both numbers by 4 which gives you the final answer of 4:7.
To sum up, question 1 is 16, question 2 is 8 and question 3 is the ratio 4:7.