The lengths of the three altitudes of a triangle are 6x,4x and 3x units respectively. if it's perimeter is 18 units then it's area is.

This is the concept of algebra, for us to calculate the area of the triangle we need the value of x. Therefore, we shall obtain this from the perimeter.

P=6x+4x+3x=18
13x=18
x=18/13
x=1.385
The length of the altitudes will be:
6x=6×1.385=8.31 
4x=4×1.385=5.54
3x=3×1.385=4.155
the area will be given by Heron's formual:
Area=√[p(p-a)(p-b)(p-c)]
p=(a+b+2)/2
=(8.31+5.54+4.155)/2
=9.0025
therefore:
A=√[9.00(9-8.31)(9-5.54)(9-4.155)
A=104.64 sq. units