We start with a circle, then we draw in the
150° America "piece of pie"


Now we calculate the number who would like
to visit America with ratio-and-proportion

Let N represent the number who would like to visit
America:

Then N is to the total 3240 people as the 150°-angle
is to the total 360 degrees in the whole circle.



Then we draw in the 90° Africa "piece of pie"



Now we calculate the number who would like
to visit Africa with ratio-and-proportion

Let N represent the number who would like to visit
Africa:

Then N is to the total 3240 people as the 90°-angle
is to the total 360 degrees in the whole circle.




Now we have accounted for 150°+90° or 240° of the 360° in the
whole circle.  Therefore if we subtract 240° from 360°, we get
120° for both the Asia and Australia pieces of pie together. 
So we will let x° be the number of degrees for the Asia piece
of pie, and then subtract x° from 120° to get 120°-x° for the 
Australia piece of pie.



We could go straight for the answer here, but so we 
can draw the pie graph accurately we calculate the angle
of the Asia piece of pie with ratio-and-proportion:

The angle of the Asia piece of pie is to the angle of 
the Australia piece of pie as 3 is to 2  

          

Therefore the angle of the Australia piece of
pie is 120°-72° or 48°



Let N represent the number who would like to visit
Asia:

Then N is to the total 3240 people as the 72°-angle
is to the total 360 degrees in the whole circle.



Let N represent the number who would like to visit
Australia:

Then N is to the total 3240 people as the 48°-angle
is to the total 360 degrees in the whole circle.



So that's the answer and the final pie graph looks like this


Edwin