Answer:
 10 units
Explanation:
Given data
 P = (3, 1) and Q = (-3, -7)
x1=3
y1=1
x2= -3
y2= -7
The expression for the distance between two coordinate is 
 d=√((x_2-x_1)²+(y_2-y_1)²)
Substitute
 d=√((-3-3)²+(-7-1)²)
 d=√((-6)²+(-8)²)
 d=√36+64
 d=√100
d=10 units
Hence the distance is 10 units