Firstly we will get the third side AB by PGT
H^2=P^2+B^2
H^2=6^2+8^2
H^2=36+64
H^2=100
H= 10 CM
Now by herons formula
s=a+b+c/2
=10+8+6/2
=24/2
=12cm
now
Area of ABC=root(s(s-a)(s-b)(s-c)
=root(12*2*4*6
=root(2*6*2*2*2*6
=2*2*6
=24cm^2
Now altitude is DC
and Area of triangle=1/2 * B * H
24=1/2 * 10 * DC
24*2 * 1/10=DC
DC=4.8cm
ADC is right angled triangle with angle D=90
BY PGT
H^2 = P^2 + B^2
6^2 = 4.8^2 + x^2
36-23.04 = x^2
x^2 = 12.96
x= root(12.96
x= 3.6 (approximately)
Hope it helped