What you do is just find the missing value of the x.
ANSWER

EXPLANATION
To find the number of balloons that are purple, we have to find six-sevenths of 35.
That is:

That is the number of balloons that are purple.
Answer: 120
You can do p/100 = is/of
40/100 = is/300
then multiply diagonally which is 40 and 300
divide by 100
or the easier way is you can multiply .4 and 300