Solution: Let the height of balloon 1 be Y 1, the height of balloon 2 be y2, and the height difference between the two balloons be y3.

y 1=x+5

y2=0.5x+ 15

y3 = y 1-y2 =(x+5)-(0.5x+ 15)= 0.5x- 10

∵30≤x≤50

When x=30, y3= 15- 10=5.

When x=50, y3=25- 10= 15.

Therefore, 5≤y3≤ 15.

Therefore, when 30 is less than or equal to x is less than or equal to 50, the maximum height difference between two balloons is 15m.