We only have so many roses, so by finding out how many are used by these bouquets, we can deduce which one is possible.
1. 3 bouquets with 5 red roses and 10 white roses in each
Since there are 3 bouquets, and there are equal amounts of roses in each bouquet, multiply these values by 3 for the total number of roses used.
3*5 red roses=15 red roses
3*10 white roses=30 white roses
This is impossible, as we only have 20 white roses. This is incorrect.
2. 4 bouquets with 3 red roses and 7 white roses in each
Repeat the same process as used above.
4*3 red roses=12 red roses
4*7 white roses=28 white roses
Once again, this is impossible, as we only have 20 white roses. Still not right.
3. 5 bouquets with 3 red roses and 4 white roses in each
Repeat the same process
5*3 red roses=15 red roses
5*4 white roses=20 white roses
These are the exact limits we have, meaning this is possible to do. This is the correct answer.
4. 5 bouquets with 10 red roses and 15 white roses in each
Just to make sure we have the right answer, lets do the same process here.
5*10 red roses=50 red roses
5*15 white roses=75 white roses
This is way over the amount of roses permitted, so this is also incorrect.
Therefore, the correct answer is 5 bouquets with 3 red roses and 4 white roses in each. I hope this helps!