You can first move the x and y variable around so it fits the standard linear equation format.
x + y/3 = 5
In order to make it look more like the standard format, you can multiply both sides of the equation by 3 to get rid of the 3 in the denominator of the y variable. It would look like this:
So 100% - 20% - 10% - 30% = 40% 40% of people were men. It says that there were 3600 men and in order to find the total amount of people, do 3600/40% or 3600/.4 Which equals 9000
