Equation of planes : 3x+4y−z=5&6x+8y−2z=15
Obviously these are parallel planes as D.C's normal to both the planes are same.
Take a point (0,0,-5) as 1st plane:
Distance of a point P(x,y,z) to plane
ax+by+cz+d=0 is given by
|ax+by+cz+d|√a2+b2+c2
Here x1=0,y1=0,z1=−5,d=−15
a=6,b=8c=−z
Distante |(2)(−5)−15|√62+82+(−2)2=5√36+64+4=5√104=52√26