STEP 1 :
Equation of parabola : y2 = 16x
On comparing with : y2 = 4ax , 4a = 16 , a = 4
STEP 2 :
P(x , 8) lies on parabola y2 = 16x & hence it must satisfy the equation of parabola
∴ 82 = 16x
x = 4 , P(4,8)
STEP 3 :
Focal distance of point P(4,8) = PS
= PM ……….. FOCUS DIRECTRIX PROPERTY
= x + a
= 4 + 4
= 8 units